Author Topic: Conservation of energy/momentum.  (Read 26139 times)

Offline chazemz

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Conservation of energy/momentum.
« on: 09/09/2017 01:11 PM »
With reference to the EM drive thread there appears to be a lot of “violates this conservation law” and “violates that conservation law” when I am of the opinion that what you are in fact doing is preserving third law. Commenting earlier on conservation of energy/momentum I put forward a simple experiment asking what would happen with a five ball newton's cradle if you raised two balls and let them go so they collided with the remaining three balls. We were in agreement that two balls must come out the other side since if one ball came out at twice the velocity momentum would be conserved but not kinetic energy I then asked if nature treats momentum and energy as the same and when nature conserves “it accounts for”.
So on this point I would like to ask a question: if we have a spaceship that has a surrounding skin that you are calling “the boundary”and I fit solar panels to the outside ( we are assuming that we have a device inside the spaceship that transfers energy/ momentum to the spaceship from the solar panels), if the energy/momentum in equals the energy/momentum stored  plus losses, since the energy/momentum comes from outside the boundary am I to assume that all is well?
For the Newtonians among you we are not looking at third law in this instance, just conservation of energy/momentum.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #1 on: 09/10/2017 05:20 PM »
So we can now place a battery in the spaceship and fit a switch. With the device switched off we can charge the battery via the solar panels. When the battery is fully charged we can jettison the solar panels and wait for a while.
I can now ask another question: The energy/momentum stored in the battery came from outside the boundary in the first instance, but when the switch is switched on nothing is passing through the boundary at that moment. So, immediately prior to switch on, is the spaceship a closed system?

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #2 on: 09/10/2017 05:36 PM »
What do you mean "momentum stored in the battery"? Batteries only store energy. The miniscule momentum that the photons impart on the solar panels is spread across the whole spacecraft.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #3 on: 09/11/2017 05:31 PM »
I think it better if I use a different example.
We have a very long spaceship and at one end is fixed a cannon. Nothing is moving in the spaceship    and since we have our boundary with no external forces acting on it, we will call this a closed system. We fire the cannon and the cannon ball starts to travel along the spaceship. The recoil of the cannon means that the spaceship will begin to move in the opposite direction to the cannon ball. But as the spaceship moves it interacts with the outside. This means that exterior forces are acting on the spaceship so it is no longer a closed system. This will continue until the cannon ball hits the opposite end of the spaceship (we will have the wall really sticky so the cannon ball sticks to it on impact) The spaceship stops moving and so returns to being a closed system.
I do not need to go into detail to explain the error of your arguments regarding conservation laws and  newtonians will be pleased that this thought experiment includes third law as well.

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #4 on: 09/11/2017 05:43 PM »
But as the spaceship moves it interacts with the outside. This means that exterior forces are acting on the spaceship so it is no longer a closed system.
So you actually aren't talking about a closed system at all, you are talking about an open system. To describe anything about this system's behavior, you need to define exactly what it is interacting with outside, and what these forces are.

I do not need to go into detail to explain the error of your arguments regarding conservation laws and  newtonians will be pleased that this thought experiment includes third law as well.
Error of what arguments? The only thing I stated is the simple fact that batteries don't store momentum. And yes, you have to respond to arguments if you want to have a conversation.

Offline whitelancer64

Re: Conservation of energy/momentum.
« Reply #5 on: 09/11/2017 06:03 PM »
Momentum and energy are not the same thing.
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Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #6 on: 09/11/2017 06:56 PM »
But as the spaceship moves it interacts with the outside. This means that exterior forces are acting on the spaceship so it is no longer a closed system.
So you actually aren't talking about a closed system at all, you are talking about an open system. To describe anything about this system's behavior, you need to define exactly what it is interacting with outside, and what these forces are.

I do not need to go into detail to explain the error of your arguments regarding conservation laws and  newtonians will be pleased that this thought experiment includes third law as well.
Error of what arguments? The only thing I stated is the simple fact that batteries don't store momentum. And yes, you have to respond to arguments if you want to have a conversation.

Well it is a closed, open, closed system. If you want to go further, take the spaceship into a region of nothing and then fire the cannon. With nothing to interact with, it will remain a closed system. So theoretically speaking you can move a closed system and conserve momentum.
I was not referring to you in the arguments. 

Momentum and energy are not the same thing.
 Mmmmm, I agree, but is momentum stored energy?

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #7 on: 09/11/2017 07:16 PM »
If you want to go further, take the spaceship into a region of nothing and then fire the cannon. With nothing to interact with, it will remain a closed system. So theoretically speaking you can move a closed system and conserve momentum.
No, the center of mass of the system will not move. You can't actually move, just rearrange the ship around that point.

I was not referring to you in the arguments. 
No one else had responded to the thread.

Mmmmm, I agree, but is momentum stored energy?
No.

Offline whitelancer64

Re: Conservation of energy/momentum.
« Reply #8 on: 09/11/2017 07:32 PM »

Momentum and energy are not the same thing.
 Mmmmm, I agree, but is momentum stored energy?

No. Momentum and kinetic energy are not the same thing either. They are related, but not at all the same.

Kinetic energy is 1/2 the product of the mass times velocity squared.
Ek = 1/2 mv^2

Momentum is mass times velocity.
p = mv

Two objects with the same kinetic energy only have the same momentum if they also have the same mass.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
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Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #9 on: 09/12/2017 12:50 PM »
It would be better if I made myself clearer. We will assume the spaceship is a closed system in the first instance.
If a spaceship was to be fitted with a device that could move the spaceship from within and the spaceship was to move within the confines of the known universe, as soon as the spaceship begins to move it can no longer be classed as a closed system.
If a spaceship was to be fitted with a device that could move the spaceship from within, in a region of nothing, the spaceship will remain a closed system.
An object that has constant momentum is storing energy.
The battery could be described as a rocket engine in that it converts stored chemical energy into kinetic energy.
I must make it clear, I am not validating EM Drive with any of the above statements.
 

Offline whitelancer64

Re: Conservation of energy/momentum.
« Reply #10 on: 09/12/2017 01:06 PM »
No. Momentum is not stored energy. For any closed system, the total momentum is always constant. Momentum cannnot be converted into a different form of energy.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
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Online meberbs

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Re: Conservation of energy/momentum.
« Reply #11 on: 09/12/2017 02:13 PM »
If a spaceship was to be fitted with a device that could move the spaceship from within and the spaceship was to move within the confines of the known universe, as soon as the spaceship begins to move it can no longer be classed as a closed system.
Not true, the spacecraft moving does not make it an open system. You had correctly mentioned previously that external forces are involved in making it an open system. You have not described any forces though. We are talking about a spacecraft in deep space. There are no forces defined on it, so it is a closed system, unless you describe external forces acting on it.

The battery could be described as a rocket engine in that it converts stored chemical energy into kinetic energy.
Momentum conservation says that this doesn't make sense. You can't just convert chemical energy to kinetic energy, you have to balance conservation of momentum by expelling some sort of exhaust.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #12 on: 09/13/2017 12:03 PM »
If a spaceship was to be fitted with a device that could move the spaceship from within and the spaceship was to move within the confines of the known universe, as soon as the spaceship begins to move it can no longer be classed as a closed system.
Not true, the spacecraft moving does not make it an open system. You had correctly mentioned previously that external forces are involved in making it an open system. You have not described any forces though. We are talking about a spacecraft in deep space. There are no forces defined on it, so it is a closed system, unless you describe external forces acting on it.

The battery could be described as a rocket engine in that it converts stored chemical energy into kinetic energy.
Momentum conservation says that this doesn't make sense. You can't just convert chemical energy to kinetic energy, you have to balance conservation of momentum by expelling some sort of exhaust.
I see your point with reference to deep space. It would be better to use the term “at first contact”, so in low earth orbit very quick; in deep space, a little longer.
The rocket engine does it by combustion, the battery would do it by using the flow of electrical energy/power..So Watts = joules = newtons. You transfer energy from the battery onto the body of the spaceship. In low earth orbit it would then change to an open system.
It would be easier if we could define when a “closed system” is a “closed system” which is what I have tried to do in the earlier posts. If we place a charged battery into the spaceship and close all the hatches, have we got a” closed system”? So another little thought experiment! We take the cannon outside the spaceship and leave a hatch open. We fire the cannon so the cannon ball flies through the hatch and then close the hatch. What have we got?. Technically it is a “closed system” since the cannon ball has not interacted with the spaceship. But we have an “open system” in waiting since we can tell the future and know what is going to happen. And as soon as we define the system as “closed” does the cannon ball become part of the system so cannot be referred to as “exterior”
With reference to the exhaust, I need to know how you define “conserve”
Would it not be better to use the term energy/momentum are always “accounted for”?

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #13 on: 09/13/2017 02:03 PM »
The rocket engine does it by combustion, the battery would do it by using the flow of electrical energy/power..So Watts = joules = newtons.
This is nonsensical. You can't just equate units that mean different things.

You transfer energy from the battery onto the body of the spaceship. In low earth orbit it would then change to an open system.
Where is the momentum balance? What specific external forces are you using? Just because it is an open system, doesn't mean that magic suddenly can happen. The open system of a satellite in LEO transfers both energy and momentum into the thin atmosphere, causing the satellite to slow down and eventually crash.

It would be easier if we could define when a “closed system” is a “closed system” which is what I have tried to do in the earlier posts. If we place a charged battery into the spaceship and close all the hatches, have we got a” closed system”? So another little thought experiment! We take the cannon outside the spaceship and leave a hatch open. We fire the cannon so the cannon ball flies through the hatch and then close the hatch. What have we got?. Technically it is a “closed system” since the cannon ball has not interacted with the spaceship. But we have an “open system” in waiting since we can tell the future and know what is going to happen. And as soon as we define the system as “closed” does the cannon ball become part of the system so cannot be referred to as “exterior”
You simply have to define what your system is. If you are going to leave the hatch open and let the cannon ball fly out you can either include the cannon ball in the system or not. If you include the cannon ball, then the center of mass of the spaceship + ball will not move, but both will fly off into infinity. If you don't include the ball, then the spacecraft transferred some energy to the ball and transferred momentum to the ball that is equal and opposite to the momentum the spacecraft ends up with. Both perspectives lead to the same result. If you are going to close the hatch before the ball can leave, then it only makes sense to consider the spacecraft and ball as a single system. You don't have to, but it makes it easier to see what would happen.

With reference to the exhaust, I need to know how you define “conserve”
Would it not be better to use the term energy/momentum are always “accounted for”?
I know someone used the phrase "account for" with you to try to get you to understand. It doesn't seem like it worked. Conserve is the standard well defined term that physicists use though, which you can look up.

I am not great at definitions, and at this point you should really just go do some research yourself, and maybe take an introductory physics class somewhere.

Basically conserve means that if you add up the momentum or the energy of some set of objects that don't interact with any other objects, it will not change with time. If they do interact with something else you can just add those objects to the system to see that momentum and energy are both still conserved. Otherwise you define the flux of momentum and energy in and out of the system as the interactions with the objects external to the system.

Offline whitelancer64

Re: Conservation of energy/momentum.
« Reply #14 on: 09/13/2017 02:41 PM »
*snip*
With reference to the exhaust, I need to know how you define “conserve”
Would it not be better to use the term energy/momentum are always “accounted for”?

In science, the word "conserve" means that the total amount is unchanged through the course of a process. The amount of energy in a given system can change forms (for example, a chemical reaction can give off heat), but the amount of energy in the system always remains the same before and after the reaction. Same with momentum, in an interaction between two bodies, the total amount of momentum always stays the same before and after the interaction.
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Offline Rocket Science

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Re: Conservation of energy/momentum.
« Reply #15 on: 09/13/2017 02:49 PM »
Please note not all collisions are equal: elastic vs inelastic collisions. A perfectly elastic collision is defined as one in which there is no loss of kinetic energy in the collision. ... Momentum is conserved in inelastic collisions, but one cannot track the kinetic energy through the collision since some of it is converted to other forms of energy.
https://www.khanacademy.org/science/physics/linear-momentum/elastic-and-inelastic-collisions/v/elastic-and-inelastic-collisions
« Last Edit: 09/13/2017 02:50 PM by Rocket Science »
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Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #16 on: 09/13/2017 03:46 PM »
You simply have to define what your system is. If you are going to leave the hatch open and let the cannon ball fly out you can either include the cannon ball in the system or not.

The cannon ball flies INTO the spaceship, then the hatch is closed.
Is it then classed as a "closed system".
If it is a "closed system" what will happen to conserve momentum in the system.

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #17 on: 09/13/2017 03:59 PM »
You simply have to define what your system is. If you are going to leave the hatch open and let the cannon ball fly out you can either include the cannon ball in the system or not.

The cannon ball flies INTO the spaceship, then the hatch is closed.
Is it then classed as a "closed system".
If it is a "closed system" what will happen to conserve momentum in the system.
If you are defining it as a closed system, then the system is spacecraft + ball. The system starts with net momentum, and ends with the same net momentum.

The definition of a system boundary is arbitrary and based on whatever makes the solution easier to calculate. Often this means finding a set of objects that can be considered a closed system.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #18 on: 09/14/2017 12:06 PM »
Jamie and I did discuss this data with Roger. He commented it was representative of what he would expect from Jamie's test rig.
But it is not representative of what would happen if the force generation stopped when the acceleration stopped. In that case, the drive would return straight back to the null position from the first peak (and oscillate around it) rather than oscillating around the forward position.

As for what could be causing the displacement, you have to remember that while it is only 2W of power, it is also only equivalent to a couple of microNewtons of force. The end of the generation of the apparent force does not correspond to the drive reaching 0 acceleration or to the end of the RF power. This is not an encouraging piece of data for the emDrive working.

I would like to introduce another thought experiment that may be helpful.
I have a long sealed box and attached to one end is a small very rapid firing machine gun (10,000 rpm) with a magazine of 10,000 rounds. I place the box on a sensitive thrust measuring device and turn the machine gun on. The box will show a slight deflection which would indicate thrust and the deflection will last for 60 seconds. If the box is taken into space and the experiment repeated, I am of the opinion that the box will initially accelerate but then the box will move at a steady (if not rapid jerky motion) rate (Not accelerate) until the magazine is exhausted.  Are we not exploiting the time lag between action and reaction which may give us a false impression on the measuring device?

Offline ppnl

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Re: Conservation of energy/momentum.
« Reply #19 on: 09/14/2017 09:26 PM »

No, there is no time lag between action and reaction. The gun fires a bullet. Action. The box is instantly pushed in the other direction. Reaction. The bullet hits the far wall. Action. The impulse of the bullet instantly stops the motion of the box. Reaction. Action and reaction are connected instantaneously.  You just have a pair of them.

The center of gravity of the box will not move at all. The box will appear to move but no matter how many bullets you use it will always move by less than the length of the box. You are just shifting weights inside the box causing its position with respect to its center of gravity to shift. The center of gravity itself does not shift. Get a broom and sweep the bullets back to the other end and the box will move back to its original position.

Your measuring device will show all of this perfectly.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #20 on: 09/15/2017 11:34 AM »
We are looking at the action, reaction of the box. The bullet has a distance to travel , therefore it will take time.
Using the level pendulum test,( no tilting) sustained deflection would be a strong indication of net thrust.
We appear to agree that although  we have a strong indication of net thrust, the device will not accelerate for the period of 60 seconds and will operate as you have said. Therefore contrary to what the test results suggest, it does not work.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #21 on: 09/16/2017 11:11 AM »
I would like to ask some questions. I am in a spacecraft (I have grip on the floor) and at one end a spring is attached to the wall. I hold the spring and begin to walk backwards, extending the spring. 1) What will happen to the spacecraft as I walk backwards? 2) What will happen to the spacecraft when I let go of the spring? 3) What will happen to the spacecraft when the spring has returned to its original state?

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #22 on: 09/16/2017 02:01 PM »
I would like to ask some questions. I am in a spacecraft (I have grip on the floor) and at one end a spring is attached to the wall. I hold the spring and begin to walk backwards, extending the spring. 1) What will happen to the spacecraft as I walk backwards? 2) What will happen to the spacecraft when I let go of the spring? 3) What will happen to the spacecraft when the spring has returned to its original state?
Honestly I think it would be more helpful for you to try to work out the answer yourself, keeping in mind that the combined center of mass of the spaceship and all objects inside it will not move. In this case that refers to the hull, you, and the spring. Drawing a diagram may help with this.

Note that to simplify things in mass-spring systems, physicists often assume that a spring has no mass, which is fine when masses attached to either end of the spring have significantly more mass than the spring. Since you are letting go of one end of the spring, there is no mass attached to that end, so you can't consider the spring massless if you want to see the dynamics of the spring retracting.

Offline kamill85

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Re: Conservation of energy/momentum.
« Reply #23 on: 09/16/2017 11:25 PM »
Related to the main topic:

Test object description: spherical object with embedded power source, with outer layer composed of disks connected to motors beneath. Motors can be remotely activated at any time.

Now, if we had two test objects of the same rest-mass, accelerated both to same speed, and then remotely activated motors of one of them, would that on object have higher kinetic energy from our point of view?
Assumption: 100% efficient motors, no heat radiation, basically 100% of the battery power gets converted into spin.

Question comes from the fact that if something gets a spin in space, for example super fast rotating black holes or neutron stars, then such objects appear to have higher mass, create "deeper" gravity well.

If true: 2 saucer shaped enclosures could house rotation rigs of circularly arranged motors with certain mass to rotate at speed = X. Rotation rigs would rotate in opposite directions, with equal speed = Y, that can be changed at any time. Central unit between the two enclosures would keep track of some target, and activate motor approaching its direction in either enclosure while its at 90'c angle until 0', leaving 0' to -90' for de-acceleration. Basically, motors would be only spinning while they are on the 180' side that points toward the target. Speeds X and Y would control thrust level?

PS. Similar "drive" was proposed for capacitors, where at 90' angle they are loaded with power and unloaded at -90'. So 180' gets rotated with empty capacitor and 180' with loaded. Electricity only gets through at c from the middle outwards to capacitor at same, horizontal line towards the target, different direction between the enclosures, hence possible motion is canceled out. In this example even if mass of capacitor grows only a little bit, the difference is directly multiplied/scaled by the rotation speed.

PPS. I am aware effects described here would be barely detectable, due to mechanical stress limiting the speeds, but if there was a way to capture similar idea in less mechanical and more "solid state" fashion, it could be something.
« Last Edit: 09/16/2017 11:59 PM by kamill85 »

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #24 on: 09/17/2017 09:54 AM »
I would like to ask some questions. I am in a spacecraft (I have grip on the floor) and at one end a spring is attached to the wall. I hold the spring and begin to walk backwards, extending the spring. 1) What will happen to the spacecraft as I walk backwards? 2) What will happen to the spacecraft when I let go of the spring? 3) What will happen to the spacecraft when the spring has returned to its original state?
Honestly I think it would be more helpful for you to try to work out the answer yourself, keeping in mind that the combined center of mass of the spaceship and all objects inside it will not move. In this case that refers to the hull, you, and the spring. Drawing a diagram may help with this.

Note that to simplify things in mass-spring systems, physicists often assume that a spring has no mass, which is fine when masses attached to either end of the spring have significantly more mass than the spring. Since you are letting go of one end of the spring, there is no mass attached to that end, so you can't consider the spring massless if you want to see the dynamics of the spring retracting.

I do like to ask questions, I find I learn things by doing so. There are other people who may be interested in the answer also and you have answered the question far better than I could have done.

Offline A_M_Swallow

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Re: Conservation of energy/momentum.
« Reply #25 on: 09/17/2017 11:48 AM »
Just a reminder.

E = m c2

Energy is equal to MASS not momentum. So it is energy-mass that is conserved. The conservation of momentum is a different conservation. When items collide two separate things are conserved at the same time, this can have some interesting side effects

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #26 on: 09/18/2017 09:26 AM »
I am on your wavelength here (no pun intended), although there is a school of thought that says a photon has momentum but no mass?

Offline dustinthewind

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Re: Conservation of energy/momentum.
« Reply #27 on: 09/18/2017 01:40 PM »

Momentum and energy are not the same thing.
 Mmmmm, I agree, but is momentum stored energy?

No. Momentum and kinetic energy are not the same thing either. They are related, but not at all the same.

Kinetic energy is 1/2 the product of the mass times velocity squared.
Ek = 1/2 mv^2

Momentum is mass times velocity.
p = mv

Two objects with the same kinetic energy only have the same momentum if they also have the same mass.

Energy is the integral of momentum with respect to velocity.  int(m*v , dv) = 1/2*m*v^2.  You can also think of it as E=F*dx --> int(m*a , dx --> m*v*dx/dt) = 1/2*m*v^2 .  Of course at higher speeds one must take into account relativistic terms.  One might claim if momentum is conserved then the sum of all momentum should also be conserved. 

PS there are extra terms of the mass of the system is changing.
« Last Edit: 09/18/2017 06:08 PM by dustinthewind »

Offline dustinthewind

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Re: Conservation of energy/momentum.
« Reply #28 on: 09/18/2017 01:55 PM »
With reference to the EM drive thread there appears to be a lot of “violates this conservation law” and “violates that conservation law” when I am of the opinion that what you are in fact doing is preserving third law. Commenting earlier on conservation of energy/momentum I put forward a simple experiment asking what would happen with a five ball newton's cradle if you raised two balls and let them go so they collided with the remaining three balls. We were in agreement that two balls must come out the other side since if one ball came out at twice the velocity momentum would be conserved but not kinetic energy I then asked if nature treats momentum and energy as the same and when nature conserves “it accounts for”.
So on this point I would like to ask a question: if we have a spaceship that has a surrounding skin that you are calling “the boundary”and I fit solar panels to the outside ( we are assuming that we have a device inside the spaceship that transfers energy/ momentum to the spaceship from the solar panels), if the energy/momentum in equals the energy/momentum stored  plus losses, since the energy/momentum comes from outside the boundary am I to assume that all is well?
For the Newtonians among you we are not looking at third law in this instance, just conservation of energy/momentum.

For newtons cradle the kinetic energy/momentum is retained in the matter during elastic collision as kinetic energy.  There is some potential flexing of bonds in the process but it will still be kinetic I think.  If you store energy in a battery, your storing that kinetic energy/momentum in chemical bonds.  After that process I think the stored energy can be converted to different systems efficiently.  Inherent inefficiencies would probably be related to different relative masses.  Newtons cradle ~ 100% efficient at conveying kinetic energy/momentum between its systems of masses. 

Edit: I think your talking about using an EM drive powered by solar panels.  Saying the EM drive will work if solar panels are used doesn't make it suddenly an open system.  The solar panels reflecting or absorbing light can get thrust that way but its inefficient and it can be stored as power.  From the stored power you could run your EM drive but how that energy acts on something that will escape the ship so it can gain momentum is still a mystery that has not yet been solved.

« Last Edit: 09/19/2017 02:26 AM by dustinthewind »

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Re: Conservation of energy/momentum.
« Reply #29 on: 09/18/2017 03:53 PM »
I am on your wavelength here (no pun intended), although there is a school of thought that says a photon has momentum but no mass?
Yes, the energy equation E = m0*c^2 uses the rest mass m0 of the object. Photons have no rest mass, but the full energy equation in special relativity is:

E^2 = (m0*c^2)^2 + (p*c)^2

Where p is the momentum.

For a massless particle, this reduces to E = p*c.

The energy equation can be rearranged for massive particles based on the relativistic momentum p =γ*m0*v as:

E = γ*m0*c^2

The relativistic mass is m = m0*γ, so this is equivalent to E = m*c^2. Note that some references just use m for rest mass, so there are 2 things that the equation E=m*c^2 can mean depending on the definition of the variables (both are true):
-Energy of an object at rest equals its rest mass times the speed of light squared.
-Total energy including kinetic of a moving object equals its relativistic mass times the speed of light squared.

Note that the definition of momentum p =γ*m0*v does not work for a massless particle, because mass is 0, but γ is infinity when velocity is the speed of light. This makes the equation E = γ*m0*c^2 meaningless for a massless particle, since you cannot calculate the result. instead you have to go to the first one and say E = p*c. Then if you want you can define a relativistic mass of a massless particle to be m = E/c^2 = p/c, but it still has no rest mass.

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Re: Conservation of energy/momentum.
« Reply #30 on: 09/26/2017 06:37 PM »
 The zero approach to conservation of momentum (what I like to call  “you can only use what god gave us”) is a newtonian third law idea that makes perfect sense. For an object to accelerate something else must decelerate or vice versa. Therefore N + -N = 0. This is why the argument will always be for there to be an exhaust of some kind. So with this in mind we can do another thought experiment:
I am travelling through nothing, I am going to give myself a direction and I am side on to the direction I am travelling. I am holding a magnet in each hand and my arms are outstretched in front of me. The poles of the magnets are opposite so when I release them they will attract each other. When I let go of the magnets one magnet will accelerate and the other magnet will decelerate. I would however like to ask a question?
If I turn so that I am facing the direction of travel and repeat the experiment, what will now happen when I release the magnets?

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Re: Conservation of energy/momentum.
« Reply #31 on: 09/26/2017 06:49 PM »
When I let go of the magnets one magnet will accelerate and the other magnet will decelerate.
Both magnets accelerate. "Decelerate" is not a generally useful term in physics, since it means "accelerate in a specific direction," and using it then causes confusion, as you are demonstrating, when acceleration is not in a direction parallel to the velocity.

If I turn so that I am facing the direction of travel and repeat the experiment, what will now happen when I release the magnets?
The exact same thing, both magnets accelerate. The are accelerating in opposite directions, so momentum is conserved. You have to remember that momentum is a vector quantity, not a scalar quantity. It has a direction. (If you aren't familiar with the concepts of scalar and vector quantities, I suggest you do some research and studying on your own.)

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #32 on: 09/26/2017 06:56 PM »
What about energy conservation?

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Re: Conservation of energy/momentum.
« Reply #33 on: 09/26/2017 07:35 PM »
What about energy conservation?
Do you have a specific question about it? The last scenario you described simply involves conversion of potential energy to kinetic energy.

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Re: Conservation of energy/momentum.
« Reply #34 on: 09/27/2017 03:40 PM »
What about energy conservation?
Do you have a specific question about it? The last scenario you described simply involves conversion of potential energy to kinetic energy.

Well there are numerous questions that can be asked but we will start with a specific one. When I let go of the magnets they will, as you have stated, accelerate towards one another. Using inverse cube we know that the rate of acceleration will rise dramatically as the distance between them decreases. So where are the magnets getting their energy/momentum from?

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Re: Conservation of energy/momentum.
« Reply #35 on: 09/27/2017 03:58 PM »
What about energy conservation?
Do you have a specific question about it? The last scenario you described simply involves conversion of potential energy to kinetic energy.

Well there are numerous questions that can be asked but we will start with a specific one. When I let go of the magnets they will, as you have stated, accelerate towards one another. Using inverse cube we know that the rate of acceleration will rise dramatically as the distance between them decreases. So where are the magnets getting their energy/momentum from?
Here is a helpful suggestion: next time you want to type "energy/momentum" DON'T

Typing that indicates that you still don't understand what you have been told repeatedly, that energy and momentum are different concepts.

What you really have is 2 separate questions, both of which I already answered:

Where do they get there momentum from?
They don't get momentum from anywhere. The total momentum of 2 magnets that both start at rest starts at 0 and remains 0 as they accelerate towards each other. Each magnet at all times has equal (magnitude) and opposite (direction) momentum to the other one.

Where do they get energy from?
The last scenario you described simply involves conversion of potential energy to kinetic energy.

P.S. Force between magnetic dipoles goes as 1/x^4, not inverse cube (1/x^3), though it gets a bit more complicated with a shaped magnet.

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Re: Conservation of energy/momentum.
« Reply #36 on: 09/27/2017 04:19 PM »
You are evading the question. The magnets will accelerate at ninety degrees to the direction of travel. As they accelerate, since they have mass, their momentum and kinetic energy will increase. Where is this energy coming from?

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Re: Conservation of energy/momentum.
« Reply #37 on: 09/27/2017 04:26 PM »
You are evading the question. The magnets will accelerate at ninety degrees to the direction of travel. As they accelerate, since they have mass, their momentum and kinetic energy will increase. Where is this energy coming from?
I didn't avoid anything. I already answered this exact question twice.

For the third time: Potential energy.
https://en.wikipedia.org/wiki/Potential_energy

And to be technical (which you should be when talking about physics) It is only their kinetic energy that increases. Total energy includes the potential energy, and therefore stays constant. And again, total momentum does not change.

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Re: Conservation of energy/momentum.
« Reply #38 on: 09/27/2017 04:44 PM »
You are evading the question. The magnets will accelerate at ninety degrees to the direction of travel. As they accelerate, since they have mass, their momentum and kinetic energy will increase. Where is this energy coming from?

You had to do "work" to bring the two magnets together. That stores potential energy. When you release them, that energy that YOU put in is released as they separate and converted into their motion.

Offline whitelancer64

Re: Conservation of energy/momentum.
« Reply #39 on: 09/27/2017 05:05 PM »
You are evading the question. The magnets will accelerate at ninety degrees to the direction of travel. As they accelerate, since they have mass, their momentum and kinetic energy will increase. Where is this energy coming from?

It seems to me the question you are trying to ask is "what causes magnets to move toward each other." The answer is their magnetic fields. The potential energy that is stored in their magnetism is converted into kinetic energy.
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Re: Conservation of energy/momentum.
« Reply #40 on: 09/27/2017 06:01 PM »
You are evading the question. The magnets will accelerate at ninety degrees to the direction of travel. As they accelerate, since they have mass, their momentum and kinetic energy will increase. Where is this energy coming from?

You had to do "work" to bring the two magnets together. That stores potential energy. When you release them, that energy that YOU put in is released as they separate and converted into their motion.
You are evading the question. The magnets will accelerate at ninety degrees to the direction of travel. As they accelerate, since they have mass, their momentum and kinetic energy will increase. Where is this energy coming from?
I didn't avoid anything. I already answered this exact question twice.

For the third time: Potential energy.
https://en.wikipedia.org/wiki/Potential_energy

And to be technical (which you should be when talking about physics) It is only their kinetic energy that increases. Total energy includes the potential energy, and therefore stays constant. And again, total momentum does not change.
I am really pleased that you have introduced potential energy, we will discuss this at a later date.
So to be technical, both of you are saying that after the two magnets have joined, the velocity of the two magnets is the same as when they were released?

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Re: Conservation of energy/momentum.
« Reply #41 on: 09/27/2017 06:30 PM »
I am really pleased that you have introduced potential energy, we will discuss this at a later date.
So to be technical, both of you are saying that after the two magnets have joined, the velocity of the two magnets is the same as when they were released?
Assuming they inelastically collide and stick together, then of course they do.

Your next question is presumably going to be what happens to the energy in this case. This question is answered by my qualification of "inelastic collision". You can read the opening of the wikipedia article on the subject for more information.

https://en.wikipedia.org/wiki/Inelastic_collision

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Re: Conservation of energy/momentum.
« Reply #42 on: 09/27/2017 07:01 PM »
No, that was not my next question. I am however getting excited here. What you are saying is that the magnets can travel the extra distance without the need for any extra energy. Just to be cautious would this not contravene conservation of energy?

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Re: Conservation of energy/momentum.
« Reply #43 on: 09/27/2017 07:03 PM »
No, that was not my next question. I am however getting excited here. What you are saying is that the magnets can travel the extra distance without the need for any extra energy. Just to be cautious would this not contravene conservation of energy?
How exactly do you think this would contradict conservation of energy?
Conservation of energy holds.

Offline whitelancer64

Re: Conservation of energy/momentum.
« Reply #44 on: 09/27/2017 07:08 PM »
No, that was not my next question. I am however getting excited here. What you are saying is that the magnets can travel the extra distance without the need for any extra energy. Just to be cautious would this not contravene conservation of energy?

Not sure why you're excited. There's utterly no need for "extra" energy. The magnets already contained all the energy needed for their movement. The total amount of energy is the same at the beginning and at the end of your thought experiment (only some of it had been converted to kinetic energy), so yes, energy is conserved.
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Re: Conservation of energy/momentum.
« Reply #45 on: 09/27/2017 07:33 PM »
 That little exchange has been very helpful. I am going on holiday for a few days . We can resume when I get back.

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Re: Conservation of energy/momentum.
« Reply #46 on: 10/12/2017 04:44 PM »
I feel we have covered enough ground to attempt a little game of chess with nature. We are all aware that it will not be played on an eight by eight board and hopefully we are all in agreement that it is impossible to get nature in checkmate. It is however possible to manoeuvre nature so that the outcome is desirable to us. We know that we must adhere to one strict rule which is conservation of energy and nature will do whatever it takes to ensure that this rule is not broken. I would like to discuss how nature sets up a repetitive cycle that conserves energy and what will happen when that cycle is broken. I am going to add the link to the video that was earlier posted in my other thread since this clearly shows this cycle in operation. There was an objection raised that the device was using the initial counter rotation to enable the end result and I would like to counter this objection by pointing out that if a counter rotating device were to be added and that if this counter rotating device were to be switched off at the earlier mentioned point (when the tube magnet is repelled by the body magnet) in the jerk then there would be no initial counter rotation. 



I will pause to allow people who have not seen the video to view it.

Offline whitelancer64

Re: Conservation of energy/momentum.
« Reply #47 on: 10/12/2017 05:15 PM »
There was already a thread dedicated to explaining to you that this noisy motor on a string doesn't violate the laws of physics. You should re-read that.

http://forum.nasaspaceflight.com/index.php?topic=43433.0
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Re: Conservation of energy/momentum.
« Reply #48 on: 10/12/2017 05:17 PM »
I feel we have covered enough ground to attempt a little game of chess with nature.
This is a terrible analogy. Nature is not the opponent in a game, if anything it is the rules of the game.

There was an objection raised that the device was using the initial counter rotation to enable the end result
You apparently did not understand a thing that was said to you. The objection is that anyone who can do force balances (or torque balances in this case) would see that the angular momentum gained by the device at the end of the video was transferred to the device from the Earth through the string.

You also only talked about conservation of energy in this post. Energy that allows the device to acquire kinetic energy clearly comes from the power supplied to the motor. The issue you are not recognizing is the completely separate question of momentum conservation (specifically angular momentum).

The rest of your description fall back to your previous issues with communication, where you refer to adding a counter rotating device without explaining what part of the device it is attached to and whether it is counter rotating relative to the body (wooden part) or the arms.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #49 on: 10/12/2017 06:32 PM »
I feel we have covered enough ground to attempt a little game of chess with nature.
This is a terrible analogy. Nature is not the opponent in a game, if anything it is the rules of the game.

There was an objection raised that the device was using the initial counter rotation to enable the end result
You apparently did not understand a thing that was said to you. The objection is that anyone who can do force balances (or torque balances in this case) would see that the angular momentum gained by the device at the end of the video was transferred to the device from the Earth through the string.

You also only talked about conservation of energy in this post. Energy that allows the device to acquire kinetic energy clearly comes from the power supplied to the motor. The issue you are not recognizing is the completely separate question of momentum conservation (specifically angular momentum).

The rest of your description fall back to your previous issues with communication, where you refer to adding a counter rotating device without explaining what part of the device it is attached to and whether it is counter rotating relative to the body (wooden part) or the arms.

Can you have kinetic energy without momentum?

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Re: Conservation of energy/momentum.
« Reply #50 on: 10/12/2017 06:44 PM »
Can you have kinetic energy without momentum?
As an example, your device has angular momentum, but its total linear momentum is 0. Pieces of it have different amounts of linear momentum if you break it up of course, and it clearly has non zero kinetic energy.

"Kinetic energy" is not a conserved quantity though. Total energy (of all types) is what is conserved, and you can clearly have energy without any momentum (both linear or angular).

It appears that you still fail to understand the basic physics concepts that have been explained to you. Perhaps you would be better served if you took an introductory physics class somewhere where they could teach you these things piece at a time.

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Re: Conservation of energy/momentum.
« Reply #51 on: 10/12/2017 06:54 PM »
angular momentum gained by the device at the end of the video was transferred to the device from the Earth through the string

How?

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Re: Conservation of energy/momentum.
« Reply #52 on: 10/12/2017 07:04 PM »
angular momentum gained by the device at the end of the video was transferred to the device from the Earth through the string

How?
The string applies a torque. This was explained to you repeatedly in the other thread. You can easily see the torque by taking your device (while it is off), and rotating it 180 degrees. You will see the string then cause it to rotate back to the rest position (and then oscillate back and forth until dissipative forces such as air resistance bring it to rest).

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Re: Conservation of energy/momentum.
« Reply #53 on: 10/12/2017 07:25 PM »
angular momentum gained by the device at the end of the video was transferred to the device from the Earth through the string

How?
The string applies a torque. This was explained to you repeatedly in the other thread. You can easily see the torque by taking your device (while it is off), and rotating it 180 degrees. You will see the string then cause it to rotate back to the rest position (and then oscillate back and forth until dissipative forces such as air resistance bring it to rest).

And I repeatedly told you that the string is not wound when the power is switched off. So the string applies no torque to the device at that moment.

Offline whitelancer64

Re: Conservation of energy/momentum.
« Reply #54 on: 10/12/2017 07:51 PM »
angular momentum gained by the device at the end of the video was transferred to the device from the Earth through the string

How?
The string applies a torque. This was explained to you repeatedly in the other thread. You can easily see the torque by taking your device (while it is off), and rotating it 180 degrees. You will see the string then cause it to rotate back to the rest position (and then oscillate back and forth until dissipative forces such as air resistance bring it to rest).

And I repeatedly told you that the string is not wound when the power is switched off. So the string applies no torque to the device at that moment.

However, the string did wind up while the device was on. Turning it off lets the string unwind, which is exactly what is seen in the video.

Additionally, even if the device were operating at a steady state in the "rest" position, simply switching the device off doesn't mean the device is no longer acting on the string, for example, the motor winds down without the interference of the magnets, that will rotate the device.

Also, since this has never been clear to me even though I asked twice in the previous thread: what is it that you are claiming this device does? You provided several contradictory statements as to how you think it works, but what exactly is it you think the end result of operating this device is?
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Re: Conservation of energy/momentum.
« Reply #55 on: 10/12/2017 07:58 PM »
angular momentum gained by the device at the end of the video was transferred to the device from the Earth through the string

How?
The string applies a torque. This was explained to you repeatedly in the other thread. You can easily see the torque by taking your device (while it is off), and rotating it 180 degrees. You will see the string then cause it to rotate back to the rest position (and then oscillate back and forth until dissipative forces such as air resistance bring it to rest).

And I repeatedly told you that the string is not wound when the power is switched off. So the string applies no torque to the device at that moment.
And you have been repeatedly told the state of the string when the device is turned off is irrelevant. While the device is on, the string applies torques. The net result of all of these torques while the device is on is the angular momentum the device has at the moment that you turn it off.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #56 on: 10/13/2017 02:56 PM »
angular momentum gained by the device at the end of the video was transferred to the device from the Earth through the string

How?
The string applies a torque. This was explained to you repeatedly in the other thread. You can easily see the torque by taking your device (while it is off), and rotating it 180 degrees. You will see the string then cause it to rotate back to the rest position (and then oscillate back and forth until dissipative forces such as air resistance bring it to rest).

And I repeatedly told you that the string is not wound when the power is switched off. So the string applies no torque to the device at that moment.
And you have been repeatedly told the state of the string when the device is turned off is irrelevant. While the device is on, the string applies torques. The net result of all of these torques while the device is on is the angular momentum the device has at the moment that you turn it off.

The state of the string when the device is switched off is everything. It is the only thing that can apply an exterior force(torque) to the device at that moment. Since the string applies zero torque at that time, it has no influence on the observed result.

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Re: Conservation of energy/momentum.
« Reply #57 on: 10/13/2017 03:25 PM »
And you have been repeatedly told the state of the string when the device is turned off is irrelevant. While the device is on, the string applies torques. The net result of all of these torques while the device is on is the angular momentum the device has at the moment that you turn it off.

The state of the string when the device is switched off is everything. It is the only thing that can apply an exterior force(torque) to the device at that moment. Since the string applies zero torque at that time, it has no influence on the observed result.
Which words in my previous post did you not understand? Your response sounds like you did not read anything other than the first sentence of my post, because you did not address the simple fact that the string had already transferred angular momentum to the device. You can clearly see in the video that the device has angular momentum just before you turn it off. Therefore, it doesn't need any more torques applied to it for it to continue to spin.

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Re: Conservation of energy/momentum.
« Reply #58 on: 10/14/2017 02:26 PM »
And you have been repeatedly told the state of the string when the device is turned off is irrelevant. While the device is on, the string applies torques. The net result of all of these torques while the device is on is the angular momentum the device has at the moment that you turn it off.

The state of the string when the device is switched off is everything. It is the only thing that can apply an exterior force(torque) to the device at that moment. Since the string applies zero torque at that time, it has no influence on the observed result.
Which words in my previous post did you not understand? Your response sounds like you did not read anything other than the first sentence of my post, because you did not address the simple fact that the string had already transferred angular momentum to the device. You can clearly see in the video that the device has angular momentum just before you turn it off. Therefore, it doesn't need any more torques applied to it for it to continue to spin.

The acceleration of the rotor arms has nothing to do with the string. Since there is no counter rotation of the body when the rotor arms accelerate just before switch off, the strings only influence is to suspend the device off the ground. It is important that you and others remain sceptical. For anyone else reading this thread feel free to correct (not insult) me at any time, being wrong is good, it means I am learning.
We could go round and round (no pun intended) with the string so I am going to move on with my next post.

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Re: Conservation of energy/momentum.
« Reply #59 on: 10/14/2017 04:06 PM »
The acceleration of the rotor arms has nothing to do with the string.
This sentence makes no sense. The system under question is the combination of the rotor arms and the body.

The torques applied by the string transfer angular momentum to that system. Through the motor and magnets, angular momentum is exchanged between the rotor and the body, but the total angular momentum preset in the system of arms+body is due to torques applied by the string.

Since there is no counter rotation of the body when the rotor arms accelerate just before switch off,
What do you mean "arms accelerate just before switch off"? Looking at the video the arms appear to be rotating with roughly constant speed just before switch off, in other words, not accelerating. Just after switch off, the arms clearly accelerate (slow down) by transferring their angular momentum to the body.
 
being wrong is good, it means I am learning.
We could go round and round (no pun intended) with the string so I am going to move on with my next post.
The string is the source of all of the angular momentum in the system. If you do not understand that, it means that you are still wrong. If you refuse to further discuss the string, it means you are not interested in learning.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #60 on: 10/15/2017 11:21 AM »
Going back to the thought experiment with the magnets. When I am facing the direction of travel and let go of the magnets, as the magnets accelerate towards each other, does their mass increase?

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Re: Conservation of energy/momentum.
« Reply #61 on: 10/15/2017 03:52 PM »
Going back to the thought experiment with the magnets. When I am facing the direction of travel and let go of the magnets, as the magnets accelerate towards each other, does their mass increase?
Rest mass is a constant. Why would you think otherwise?

The relevant speeds are slow enough that relativity is not relevant, so it is not worth bringing in the confusion of relativistic mass, especially given your apparent continued lack of understanding of basic classical physics.

Also, you have completely changed the topic again, are you not interested in understanding why your device is useless?

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Re: Conservation of energy/momentum.
« Reply #62 on: 10/15/2017 04:25 PM »
Going back to the thought experiment with the magnets. When I am facing the direction of travel and let go of the magnets, as the magnets accelerate towards each other, does their mass increase?

No.


You are only converting potential energy into kinetic energy. Thus the energy of the entire system has not changed and so mass has not changed from a relativistic point of view. Which direction you are facing is irrelevant.

If you were to let the magnets collide thus converting the kinetic energy into thermal energy and then let that thermal energy radiate away then the mass of the system would decrease. If you were then to pull the magnets apart thus adding potential energy to the system then their mass would increase.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #63 on: 10/16/2017 11:34 AM »
There are some points to think about. With regard to two magnets attracting each other, could anyone advise me on a situation I am thinking about. I am in a small spacecraft that is positioned 50 meters from a space station that I need to get to. I have no engines and it would appear that my situation is hopeless. I do have a basic understanding of classical physics. On board I have two magnets so I hatch a cunning plan. I fix myself to the spacecraft and fix one of the magnets to myself and pull the other magnet away from the one that is attached to me. I know that the magnets attract with equal magnitude and opposite in direction so the spacecraft will not move (see bootstrapping) when I do this. However when I let the magnet go I can now use this attraction to help me. As the free magnet accelerates towards me, due to third law, I and so the spacecraft will move towards the free magnet, reducing the distance between me and the space station by a tiny amount. If I repeat this process many times I am able to reach my destination with no exhaust. So using classical physics it is easy to achieve what some people believe to be impossible?

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #64 on: 10/16/2017 02:12 PM »
I fix myself to the spacecraft and fix one of the magnets to myself and pull the other magnet away from the one that is attached to me. I know that the magnets attract with equal magnitude and opposite in direction so the spacecraft will not move
This description is wrong. In order to move the one magnet, you push the outer wall of the spacecraft in the other direction. When the magnets get attracted back together it just moves the spacecraft back to its original position.

A relevant concept is center of mass. The center of mass of the spacecraft plus you plus the magnets will remain stationary unless an external force is applied to the system. Rearranging the mass inside can make the hull shift slightly, but it will shift back upon restoring the mass inside to the original position.

Offline ppnl

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Re: Conservation of energy/momentum.
« Reply #65 on: 10/16/2017 05:44 PM »
There are some points to think about. With regard to two magnets attracting each other, could anyone advise me on a situation I am thinking about. I am in a small spacecraft that is positioned 50 meters from a space station that I need to get to. I have no engines and it would appear that my situation is hopeless. I do have a basic understanding of classical physics. On board I have two magnets so I hatch a cunning plan. I fix myself to the spacecraft and fix one of the magnets to myself and pull the other magnet away from the one that is attached to me. I know that the magnets attract with equal magnitude and opposite in direction so the spacecraft will not move (see bootstrapping) when I do this. However when I let the magnet go I can now use this attraction to help me. As the free magnet accelerates towards me, due to third law, I and so the spacecraft will move towards the free magnet, reducing the distance between me and the space station by a tiny amount. If I repeat this process many times I am able to reach my destination with no exhaust. So using classical physics it is easy to achieve what some people believe to be impossible?

Actually when you pull the magnets apart the ship will appear to move. This is because you are rearranging the masses around the center of mass. The center of mass will not move but its position relative to the ship will. This will happen even if the objects aren't magnets. All that matters is that you are moving masses.

When you let the magnet go the magnets go back to their starting place and the ship does as well. Again the magnetism does not matter. All that matters is that you are moving masses. You can do it with magnetic fields, springs or air currents. If you move masses the ship will appear to shift. If you move masses back the ship will appear to shift back. What matters is that the center of mass will not shift at all. Ever.

Again the ship will wiggle back and forth by a tiny amount but the center of mass will not move.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #66 on: 10/16/2017 07:14 PM »
The magnets apply equal and opposite forces when they are pulled apart, it is called statics. When I am holding the magnet it is part of my system. When I let it go.It is external to me. You are expending energy to produce baby steps of motion, think of the cannon. The space craft will move and eventually reach the space station.

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #67 on: 10/16/2017 07:34 PM »
The magnets apply equal and opposite forces when they are pulled apart, it is called statics. When I am holding the magnet it is part of my system. When I let it go.It is external to me. You are expending energy to produce baby steps of motion, think of the cannon. The space craft will move and eventually reach the space station.
It is not called "statics." Things are moving, which is the opposite of static (the term is dynamics). The simple fact is that to push the magnet away, you and the hull of the spacecraft must move in the opposite direction.

You cannot change the definition of system midway. The magnet is always internal to the spacecraft in this situation.

It has been a while since you have so much as directly addressed a point made by anyone in this thread. Are you actually interested in learning how mechanics works, or are you going to keep repeating incorrect descriptions  while ignoring the correct explanations?

Offline ppnl

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Re: Conservation of energy/momentum.
« Reply #68 on: 10/16/2017 10:05 PM »
The magnets apply equal and opposite forces when they are pulled apart, it is called statics. When I am holding the magnet it is part of my system. When I let it go.It is external to me. You are expending energy to produce baby steps of motion, think of the cannon. The space craft will move and eventually reach the space station.

Every force has an equal and opposite reaction force. You cannot push on something without it pushing back. If you are floating in mid air and you pull the magnets apart you will not move as the forces cancel out. If you let them pull back together you still will not move and the forces still cancel out. The spaceship around you will not move as it is not connected in any way.

If you are attached to the spaceship and one of the magnets is also then when you pull the magnets apart the spaceship will move. Even if the objects you use aren't magnetic and you pull them apart the ship will move. It makes no difference if there is a magnetic field, spring, rubber band or nothing at all. All you are doing is changing the center of mass of the ship by moving the massive objects. All you can do is make the ship wiggle back and forth by a tiny amount as you move the masses apart and back together. All you are doing is shifting the ship with respect to its center of mass. 

You only have an intuitive grasp of mechanics and your intuition is just wrong. The cannon example shows how bad you have it wrong. The cannon is attached to the Earth so when you fire the cannon in one direction it shoves the entire earth in the other by a tiny amount. When the cannon ball hits the earth it cancels the motion of the cannon and the tiny motion of the Earth. Both are in different positions now. The Earth has moved by only a tiny amount. When you carry the cannon ball back to the cannon you drag the Earth back to its original position as well. In the end everything is back where it started. And just like with the space ship you have only moved the Earth with respect to the center of mass of the Earth ball system. The center of mass did not change at all as the Earth wiggles back and forth.


Offline Bob012345

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Re: Conservation of energy/momentum.
« Reply #69 on: 10/17/2017 06:17 PM »
There are some points to think about. With regard to two magnets attracting each other, could anyone advise me on a situation I am thinking about. I am in a small spacecraft that is positioned 50 meters from a space station that I need to get to. I have no engines and it would appear that my situation is hopeless. I do have a basic understanding of classical physics. On board I have two magnets so I hatch a cunning plan. I fix myself to the spacecraft and fix one of the magnets to myself and pull the other magnet away from the one that is attached to me. I know that the magnets attract with equal magnitude and opposite in direction so the spacecraft will not move (see bootstrapping) when I do this. However when I let the magnet go I can now use this attraction to help me. As the free magnet accelerates towards me, due to third law, I and so the spacecraft will move towards the free magnet, reducing the distance between me and the space station by a tiny amount. If I repeat this process many times I am able to reach my destination with no exhaust. So using classical physics it is easy to achieve what some people believe to be impossible?

There are a few ways I can think of to get back to the station using the magnets. If you had a 50m+ string you could throw one of the magnets to the station and hope it attaches. Then you can gently pull yourself towards it. But in the whole process, the center of mass remains stationary. Or, you could throw both magnets in the opposite direction to gain a small velocity towards the station but the center of mass still remains stationary. Or, if you're truly doomed, you could break one of the magnets to make a sharp edge and then poke a small hole in your spacesuit and use the escaping air as a rocket to close the gap yet even then the center of mass remains stationary! But you need to be quick about getting back. :)
« Last Edit: 10/17/2017 06:21 PM by Bob012345 »

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #70 on: 10/18/2017 01:16 PM »
Going back to the thought experiment with the magnets. When I am facing the direction of travel and let go of the magnets, as the magnets accelerate towards each other, does their mass increase?

No.


You are only converting potential energy into kinetic energy. Thus the energy of the entire system has not changed and so mass has not changed from a relativistic point of view. Which direction you are facing is irrelevant.

If you were to let the magnets collide thus converting the kinetic energy into thermal energy and then let that thermal energy radiate away then the mass of the system would decrease. If you were then to pull the magnets apart thus adding potential energy to the system then their mass would increase.
In the first instance you are expending energy and storing it as potential energy, so yes.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #71 on: 10/18/2017 01:23 PM »
The magnets apply equal and opposite forces when they are pulled apart, it is called statics. When I am holding the magnet it is part of my system. When I let it go.It is external to me. You are expending energy to produce baby steps of motion, think of the cannon. The space craft will move and eventually reach the space station.

Every force has an equal and opposite reaction force. You cannot push on something without it pushing back. If you are floating in mid air and you pull the magnets apart you will not move as the forces cancel out. If you let them pull back together you still will not move and the forces still cancel out. The spaceship around you will not move as it is not connected in any way.

If you are attached to the spaceship and one of the magnets is also then when you pull the magnets apart the spaceship will move. Even if the objects you use aren't magnetic and you pull them apart the ship will move. It makes no difference if there is a magnetic field, spring, rubber band or nothing at all. All you are doing is changing the center of mass of the ship by moving the massive objects. All you can do is make the ship wiggle back and forth by a tiny amount as you move the masses apart and back together. All you are doing is shifting the ship with respect to its center of mass. 

You only have an intuitive grasp of mechanics and your intuition is just wrong. The cannon example shows how bad you have it wrong. The cannon is attached to the Earth so when you fire the cannon in one direction it shoves the entire earth in the other by a tiny amount. When the cannon ball hits the earth it cancels the motion of the cannon and the tiny motion of the Earth. Both are in different positions now. The Earth has moved by only a tiny amount. When you carry the cannon ball back to the cannon you drag the Earth back to its original position as well. In the end everything is back where it started. And just like with the space ship you have only moved the Earth with respect to the center of mass of the Earth ball system. The center of mass did not change at all as the Earth wiggles back and forth.


If the magnet is attracted to you, then you are attracted to the magnet, think force pairing. Yes, you are correct, when you pull the magnets apart the forces will cancel out.
I placed the cannon in a spacecraft so cannot comment further on this.
One error though, I think it incorrect to use the word "external" as you are still connected by the flux lines.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #72 on: 10/18/2017 01:38 PM »
There are some points to think about. With regard to two magnets attracting each other, could anyone advise me on a situation I am thinking about. I am in a small spacecraft that is positioned 50 meters from a space station that I need to get to. I have no engines and it would appear that my situation is hopeless. I do have a basic understanding of classical physics. On board I have two magnets so I hatch a cunning plan. I fix myself to the spacecraft and fix one of the magnets to myself and pull the other magnet away from the one that is attached to me. I know that the magnets attract with equal magnitude and opposite in direction so the spacecraft will not move (see bootstrapping) when I do this. However when I let the magnet go I can now use this attraction to help me. As the free magnet accelerates towards me, due to third law, I and so the spacecraft will move towards the free magnet, reducing the distance between me and the space station by a tiny amount. If I repeat this process many times I am able to reach my destination with no exhaust. So using classical physics it is easy to achieve what some people believe to be impossible?

There are a few ways I can think of to get back to the station using the magnets. If you had a 50m+ string you could throw one of the magnets to the station and hope it attaches. Then you can gently pull yourself towards it. But in the whole process, the center of mass remains stationary. Or, you could throw both magnets in the opposite direction to gain a small velocity towards the station but the center of mass still remains stationary. Or, if you're truly doomed, you could break one of the magnets to make a sharp edge and then poke a small hole in your spacesuit and use the escaping air as a rocket to close the gap yet even then the center of mass remains stationary! But you need to be quick about getting back. :)

The rules of the game were that nothing leaves the spacecraft, so on a technical point I cannot award you any marks. However thought experiments are designed to make you think and you have certainly done this. So I am going to award you two bonus marks for effort.
On a more serious note, By using third law you can use the potential energy of the stretched flux lines as they contract to move an object from within. The time of the movement is very short but the device overcomes this time constraint. I have copied my words from the earlier thread so people can compare them with the video .

The rotor arm magnet rotates into the repelling magnet field of the body magnet. As the distance between the two magnets decreases, the repelling force will increase. The repelling force of the body magnet will act upon the rotor arms, causing them to decelerate which can easily be seen on the video. If we apply third law, the rotor arm magnet must therefore apply the same increasing repelling force on the body magnet. This repelling force must therefore restrict the body's attempts to counter rotate. Since the body/stator is applying the load to the rotor arms/armature then the body cannot counter rotate.  We are at the point where the rotor arm has just enough momentum left to move across the body magnet. The magnetic potential energy in the body magnet and the rotor magnet is released and the rotor magnet is accelerated down the tube, which you can hear on the video. The motor is now free to accelerate and again, using classical physics, we know what should happen. As the rotor arms accelerate a force should be applied to the body causing the body to counter rotate. But as you can see in the video, the body does not counter rotate. This means that there is a counter force acting on the body which stops it counter rotating. There is a slight oscillation in the body but, if we refer to the slinky experiment, we can use statics to explain this process. 
So, as the magnets are forced together, load is applied to the motor. If we look at armature reaction, we will see that, due to the load, the main field flux lines will distort and shift the Magnetic Neutral Axis in the opposite direction to rotation. As stated earlier, the body cannot move since it is effectively pushing against itself. It is easier to visualize the movement of the M.N.A so that when the tube magnet accelerates down the tube, load will rapidly drop which will cause the main field flux lines to shorten and the M.N.A will now move in the direction of rotation. This will drag the body in the direction of rotation.

We now have the required situation where the body is attempting to move in the direction of rotation. At the same time the rotor arms apply the counter force as they accelerate.

So there you have it. A very simple device. Everything that has been explained is known and can be easily accessed. All the information can be easily found on the internet  or in any electrical engineering textbook.
I will go through the video in detail :-
1) The body is at rest and the nearest tube magnet has been pushed down the tube to allow for starting.
2) Power is switched on, the rotor arms accelerate and the body counter-rotates, winding the string.
3) Jerk cycle takes effect, resulting in no counter-rotation of the body.
4) The string now unwinds, so the device swings back and forth (string winding and unwinding) until it returns to its rest position (i.e. string is not wound).
5) Transfer of momentum as observed, device moves in the direction of the rotor arms.

If you turn the power off when the device has returned to its rest position at exactly the moment the tube magnet begins to accelerate down the tube when facing the body magnet, the device will not move, so there is no stored energy in the string at this point.

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #73 on: 10/18/2017 03:05 PM »
Going back to the thought experiment with the magnets. When I am facing the direction of travel and let go of the magnets, as the magnets accelerate towards each other, does their mass increase?

No.


You are only converting potential energy into kinetic energy. Thus the energy of the entire system has not changed and so mass has not changed from a relativistic point of view. Which direction you are facing is irrelevant.

If you were to let the magnets collide thus converting the kinetic energy into thermal energy and then let that thermal energy radiate away then the mass of the system would decrease. If you were then to pull the magnets apart thus adding potential energy to the system then their mass would increase.
In the first instance you are expending energy and storing it as potential energy, so yes.
You are not "expending energy" you are changing the form of the energy. Energy in the system is constant. Also, I do not know what you mean by "first instance" because only one situation was described, and contrary to your most recent post, it starts with potential energy and converts it to kinetic.

On a more serious note, By using third law you can use the potential energy of the stretched flux lines as they contract to move an object from within.
False. You cannot move an object from within except to shift the mass distribution around the stationary center of mass, and neither magnetic field lines nor any form of energy have anything to do with this. 

The time of the movement is very short but the device overcomes this time constraint.
The constraint is simply that the center of mass does not move, and there is no overcoming this constraint.

The rotor arm magnet rotates into the repelling magnet field of the body magnet. As the distance between the two magnets decreases, the repelling force will increase. The repelling force of the body magnet will act upon the rotor arms, causing them to decelerate which can easily be seen on the video. If we apply third law, the rotor arm magnet must therefore apply the same increasing repelling force on the body magnet. This repelling force must therefore restrict the body's attempts to counter rotate.
It does not "restrict the body's attempts to counter rotate." It simply transfers angular momentum from the arms to the body. The body already is rotating the opposite direction of the arms with equal magnitude of angular momentum. The action of the magnets slows down both the arms and the body, reducing the amount of angular momentum in both by the same amount. This interaction does not change the total angular momentum in the arms plus the body from 0.

I will stop pointing out the wrong things in your description here, because what you have said so far is so wrong, the rest ceases to have any meaning.

So there you have it. A very simple device.
Yes, it is a relatively simple device, so it is strange that you continue to make such completely wrong statements about it.

Everything that has been explained is known and can be easily accessed. All the information can be easily found on the internet  or in any electrical engineering textbook.
Yes, what is needed to understand your device is easily available, but you seem to have not read any of it. For example, you keep using the word "force" when you should be using the word "torque."


I will go through the video in detail :-
1) The body is at rest and the nearest tube magnet has been pushed down the tube to allow for starting.
2) Power is switched on, the rotor arms accelerate and the body counter-rotates, winding the string.
Good so far

3) Jerk cycle takes effect, resulting in no counter-rotation of the body.
Not "no counter rotation of the body", but a balance between the torque applied by the motor and the opposite torque applied by the magnets, so that the relative rotation speed between the arms and body is roughly fixed (if you average out the jerks)

A simpler way to accomplish the same thing without the magnets is either use a motor designed to operate at a fixed slower speed, or to apply less power to the motor so that its internal friction limits its speed to a lower value.

4) The string now unwinds, so the device swings back and forth (string winding and unwinding) until it returns to its rest position (i.e. string is not wound).
You keep ignoring that during this step, the string applies a torque to the body. The body transfers some of this angular momentum to the arms, maintaining the rotational speed difference that balances the effect of the arms and the motor.

5) Transfer of momentum as observed, device moves in the direction of the rotor arms.
This angular momentum originally came from the torques applied by the string.

Edit: fix quote tags
« Last Edit: 10/18/2017 05:35 PM by meberbs »

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #74 on: 10/18/2017 03:32 PM »
You cannot have things both ways, either classical physics is correct or it is wrong. When I let go of the magnet will I be attracted to it as it is attracted to me?

Offline Bob012345

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Re: Conservation of energy/momentum.
« Reply #75 on: 10/18/2017 05:32 PM »
You cannot have things both ways, either classical physics is correct or it is wrong. When I let go of the magnet will I be attracted to it as it is attracted to me?

Still not clear what you are trying to achieve. Are you claiming to generate more rotational energy than the energy you put into the device? Can you plainly state in one simple sentence what the device is supposed to do?

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Re: Conservation of energy/momentum.
« Reply #76 on: 10/18/2017 05:44 PM »
You cannot have things both ways, either classical physics is correct or it is wrong. When I let go of the magnet will I be attracted to it as it is attracted to me?
Classical physics is correct. You keep describing things contrary to classical physics though.

You are the one trying to have it both ways. You want to be attracted to the magnet as it is attracted to you (which you are), but you want to ignore that when you push the magnet away from you, you get pushed back as well. You are applying a force to the magnet greater than the attraction between the 2 magnets to push it away. This means by Newton's third law that it applies an equal and opposite force on you which is therefore also greater than the force of attraction, making you move away as well (to rephrase for clarity, you move in the opposite direction as the direction you pushed magnet).

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #77 on: 10/18/2017 07:05 PM »
You cannot have things both ways, either classical physics is correct or it is wrong. When I let go of the magnet will I be attracted to it as it is attracted to me?
Classical physics is correct. You keep describing things contrary to classical physics though.

You are the one trying to have it both ways. You want to be attracted to the magnet as it is attracted to you (which you are), but you want to ignore that when you push the magnet away from you, you get pushed back as well. You are applying a force to the magnet greater than the attraction between the 2 magnets to push it away. This means by Newton's third law that it applies an equal and opposite force on you which is therefore also greater than the force of attraction, making you move away as well (to rephrase for clarity, you move in the opposite direction as the direction you pushed magnet).

Nice try, you have changed pull to push. You need to think about what you are proposing. If by pulling the magnets apart I generate a force in the opposite direction, by holding the magnet away from me there would be no opposing force so the spacecraft would glide over to the space station or carry on into the great unknown. How can equal and opposite be greater on one side?

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Re: Conservation of energy/momentum.
« Reply #78 on: 10/18/2017 07:48 PM »
You cannot have things both ways, either classical physics is correct or it is wrong. When I let go of the magnet will I be attracted to it as it is attracted to me?
Classical physics is correct. You keep describing things contrary to classical physics though.

You are the one trying to have it both ways. You want to be attracted to the magnet as it is attracted to you (which you are), but you want to ignore that when you push the magnet away from you, you get pushed back as well. You are applying a force to the magnet greater than the attraction between the 2 magnets to push it away. This means by Newton's third law that it applies an equal and opposite force on you which is therefore also greater than the force of attraction, making you move away as well (to rephrase for clarity, you move in the opposite direction as the direction you pushed magnet).

Nice try, you have changed pull to push.
I changed nothing, but you seem to have no idea what the words you are using mean.

Pull and push both mean "apply a force to." Pull would be applying a force towards you, and push would be applying a force away from you. In the situation you have described, both you and "magnet A" are attached to the wall of your ship. You described moving "magnet B" away from you, the general term to describe this direction is push. I ignored your contradictory use of the word pull, since the direction is obvious, and the only other part is the same for both push and pull, you are applying a force.

If by pulling the magnets apart I generate a force in the opposite direction, by holding the magnet away from me there would be no opposing force so the spacecraft would glide over to the space station or carry on into the great unknown. How can equal and opposite be greater on one side?

You need to think about what you are saying, or maybe just go take an introductory physics course.

You are the one that is saying that "equal and opposite are greater on one side." Since the forces are equal and opposite, how could you move anywhere?

If you hold the magnet out at arm's length, there are 4 forces at play. Magnet A is attracting magnet B. Magnet B is attracting magnet A (opposite direction). You are applying a contact force to magnet B pushing it away from you, countering its attraction to magnet A. Magnet B applies an equal and opposite contact force on you, countering the magnetic force that otherwise would pull magnet A (along with you and the spacecraft) towards magnet B. Nothing is moving.

Starting from the position with the magnets touching, to separate them, you apply a force to move magnet B away, which in turn makes you move in the opposite direction as well. You continue to apply a force that balances the magnetic attraction to keep magnet B moving away, and you moving away from magnet B. (Balanced forces at this point so no acceleration, just constant velocity motion.) When you reach arm's length, you briefly stop applying this force to allow the magnetic attraction between A and B to stop you from moving further from B and B from moving further from you. (Possibly you apply a force in the opposite direction than you had been to bring you and magnet B to rest faster). Once you have done this, neither you nor magnet B are moving and you are in the static situation I described above.

To probably save some unnecessary back and forth: Do not use the word energy in replying to this post. Energy is not relevant to this description, only forces and momentum. I could describe the energy in this situation, but it is irrelevant and a distraction if you don't first understand what I have said here.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #79 on: 10/20/2017 02:42 PM »




To probably save some unnecessary back and forth: Do not use the word energy in replying to this post. Energy is not relevant to this description, only forces and momentum. I could describe the energy in this situation, but it is irrelevant and a distraction if you don't first understand what I have said here.

[/quote]

Energy is NEVER irrelevant.

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Re: Conservation of energy/momentum.
« Reply #80 on: 10/20/2017 03:00 PM »
Energy is NEVER irrelevant.
Energy is an important concept, but it is in fact irrelevant to my description of the forces and how they conserve momentum.

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Re: Conservation of energy/momentum.
« Reply #81 on: 10/21/2017 10:04 AM »
So we can use potential energy with attraction forces to move an object without exhaust. But using attraction will only give us a short time scale. To extent the time we need to use repelling forces and we can look at various scenarios.
We will use a hollow spacecraft and have two scenarios, one with permanent magnets and one with electromagnets. We will attach two counter rotating motors to the hull and fix a wheel to each motor. A short distance from the motors we will attach two wheels to the hull and connect the wheels by means of two belts. We then attach a permanent magnet to each belt and a permanent magnet to the hull half way along the straight section of the belt. We turn the motors on and the belt magnets begin to move in the same direction.  The motors will turn in opposite directions. When the belt magnets are forced into the repelling magnetic fields of the body magnets they will repel with equal and opposite force so the spacecraft will not move. As the belt magnets pass across the hull magnets they will receive a push from the hull magnets and vice versa. So will the body be pushed back after each interaction and secondly if we switch the motors off just as the belt magnets pass across the body magnets what will happen?
With the electromagnets we can switch the motors off as the magnets approach one another so causing them to transfer momentum through  collision. We then turn the electromagnets off and turn the motors on and then turn the electromagnets back on at the right time. How can the belt magnets negate the forces that we know will be applied to the hull?

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #82 on: 10/21/2017 11:00 AM »
Can we use attraction forces as well with the motors?

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #83 on: 10/21/2017 03:55 PM »
So we can use potential energy with attraction forces to move an object without exhaust.
No. You have been told this repeatedly, and not acknowledged it. Do you know what the phrase "center of mass will not move" means? Specifically are you even familiar with the concept of "center of mass"?

When the belt magnets are forced into the repelling magnetic fields of the body magnets they will repel with equal and opposite force so the spacecraft will not move. As the belt magnets pass across the hull magnets they will receive a push from the hull magnets and vice versa.
You are referring to 3 sets of magnets here, "body" "hull" and "belt" but you only described placing 2 sets, the "hull" and the "belt" for now I am going to assume you that body and hull refer to the same thing, if that is not true, you are going to need to provide a new description that isn't incomplete. (a diagram would help)

So will the body be pushed back after each interaction
No, because the forces are equal and opposite. The magnets on the belt which is taut between the wheels transfer the force applied to them to the wheels, which are rigidly connected to the motors which are rigidly connect to the hull, so the hull has equal and opposite forces applied to it and does not move.

and secondly if we switch the motors off just as the belt magnets pass across the body magnets what will happen?
Nothing. The equal and opposite forces would be constant instead of periodic, still nothing would move.

With the electromagnets we can switch the motors off as the magnets approach one another so causing them to transfer momentum through  collision.
How would anything collide? You have not described anything with the freedom of movement to collide with something else.

Your entire setup is a Rube Goldberg machine with no apparent purpose other than trying to hide your misunderstanding of physics by making the setup complicated. Rather than changing topic yet again why don't you go back to the situation of just 2 magnets, one attached to you, and one that you push away and then allow it to be attracted back to you. I provided a detailed description of the forces in that situation, and you have not indicated if you understood that post at all.

Offline Bob012345

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Re: Conservation of energy/momentum.
« Reply #84 on: 10/21/2017 04:35 PM »
So we can use potential energy with attraction forces to move an object without exhaust.

Sure you can... If the potential energy is with respect to something outside of your device like the gravitational attraction of a planet such as when doing an Oberth maneuver but not internally to your device.

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Re: Conservation of energy/momentum.
« Reply #85 on: 10/21/2017 04:37 PM »
So we can use potential energy with attraction forces to move an object without exhaust.
No. You have been told this repeatedly, and not acknowledged it. Do you know what the phrase "center of mass will not move" means? Specifically are you even familiar with the concept of "center of mass"?

When the belt magnets are forced into the repelling magnetic fields of the body magnets they will repel with equal and opposite force so the spacecraft will not move. As the belt magnets pass across the hull magnets they will receive a push from the hull magnets and vice versa.
You are referring to 3 sets of magnets here, "body" "hull" and "belt" but you only described placing 2 sets, the "hull" and the "belt" for now I am going to assume you that body and hull refer to the same thing, if that is not true, you are going to need to provide a new description that isn't incomplete. (a diagram would help)

So will the body be pushed back after each interaction
No, because the forces are equal and opposite. The magnets on the belt which is taut between the wheels transfer the force applied to them to the wheels, which are rigidly connected to the motors which are rigidly connect to the hull, so the hull has equal and opposite forces applied to it and does not move.

and secondly if we switch the motors off just as the belt magnets pass across the body magnets what will happen?
Nothing. The equal and opposite forces would be constant instead of periodic, still nothing would move.

With the electromagnets we can switch the motors off as the magnets approach one another so causing them to transfer momentum through  collision.
How would anything collide? You have not described anything with the freedom of movement to collide with something else.

Your entire setup is a Rube Goldberg machine with no apparent purpose other than trying to hide your misunderstanding of physics by making the setup complicated. Rather than changing topic yet again why don't you go back to the situation of just 2 magnets, one attached to you, and one that you push away and then allow it to be attracted back to you. I provided a detailed description of the forces in that situation, and you have not indicated if you understood that post at all.

Are you saying that when the motor on the device is switched off the rotor arms do not collide with the body magnet?
The word is PULL. Why do you keep misquoting?
I have read your post but you keep saying push not PULL, You have said that the forces are opposite(push and pull) so I can only conclude that the opposite to what you say is happening, please clarify.

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Re: Conservation of energy/momentum.
« Reply #86 on: 10/21/2017 04:47 PM »
So we can use potential energy with attraction forces to move an object without exhaust.

Sure you can... If the potential energy is with respect to something outside of your device like the gravitational attraction of a planet such as when doing an Oberth maneuver but not internally to your device.

I am in space and am holding the ends of a spring. I PULL on the spring and stretch the spring. The spring applies an equal and opposite force on each hand so I do not move. I let go of the spring. Please, please, tell me and everyone reading this thread that the spring when it is contracting does NOT apply a force on the hand that is holding the one end of the spring.

Offline Bob012345

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Re: Conservation of energy/momentum.
« Reply #87 on: 10/21/2017 05:29 PM »
So we can use potential energy with attraction forces to move an object without exhaust.

Sure you can... If the potential energy is with respect to something outside of your device like the gravitational attraction of a planet such as when doing an Oberth maneuver but not internally to your device.

I am in space and am holding the ends of a spring. I PULL on the spring and stretch the spring. The spring applies an equal and opposite force on each hand so I do not move. I let go of the spring. Please, please, tell me and everyone reading this thread that the spring when it is contracting does NOT apply a force on the hand that is holding the one end of the spring.

The force the spring applies to both hands when stretched disappears the instant one hand let's go. Any residual effects that happen due to potential energy stored in the spring and the muscles of both arms won't end up moving the center of mass of the system.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #88 on: 10/21/2017 05:50 PM »
So we can use potential energy with attraction forces to move an object without exhaust.

Sure you can... If the potential energy is with respect to something outside of your device like the gravitational attraction of a planet such as when doing an Oberth maneuver but not internally to your device.

I am in space and am holding the ends of a spring. I PULL on the spring and stretch the spring. The spring applies an equal and opposite force on each hand so I do not move. I let go of the spring. Please, please, tell me and everyone reading this thread that the spring when it is contracting does NOT apply a force on the hand that is holding the one end of the spring.

The force the spring applies to both hands when stretched disappears the instant one hand let's go. Any residual effects that happen due to potential energy stored in the spring and the muscles of both arms won't end up moving the center of mass of the system.

I asked will the contracting spring apply a force to the one hand?

Offline Bob012345

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Re: Conservation of energy/momentum.
« Reply #89 on: 10/21/2017 05:53 PM »
So we can use potential energy with attraction forces to move an object without exhaust.

Sure you can... If the potential energy is with respect to something outside of your device like the gravitational attraction of a planet such as when doing an Oberth maneuver but not internally to your device.

I am in space and am holding the ends of a spring. I PULL on the spring and stretch the spring. The spring applies an equal and opposite force on each hand so I do not move. I let go of the spring. Please, please, tell me and everyone reading this thread that the spring when it is contracting does NOT apply a force on the hand that is holding the one end of the spring.

The force the spring applies to both hands when stretched disappears the instant one hand let's go. Any residual effects that happen due to potential energy stored in the spring and the muscles of both arms won't end up moving the center of mass of the system.

I asked will the contracting spring apply a force to the one hand?

The force exists before the spring is let go but not after. So, I believe no, the spring doesn't apply a force to the hand that remains holding it.

Offline nacnud

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Re: Conservation of energy/momentum.
« Reply #90 on: 10/21/2017 05:55 PM »
Then it's a two body problem, one hand and the spring and the hand that let go.

One hand and the spring will move one way <     > the other hand will move the other way

But the centre of mass of the combined system (both hands and the spring) will stay in the same place.
 

Offline Phil Stooke

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Re: Conservation of energy/momentum.
« Reply #91 on: 10/21/2017 06:15 PM »
Live empirically!  No need to ask people what they think about this.  Build a model of the system you are thinking of.  It might be suspended above an air table or floating on still water.  Use a small radio-controlled actuator to release the end of the spring.  Run the experiment and report back to us. 

Offline nacnud

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Re: Conservation of energy/momentum.
« Reply #92 on: 10/21/2017 06:19 PM »
If you are not afraid of simple maths, try reading this, Collisions

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #93 on: 10/21/2017 08:44 PM »
Are you saying that when the motor on the device is switched off the rotor arms do not collide with the body magnet?
What rotor arms? you didn't describe any rotor arms in your post, and if you are somehow referring to the device that you previously were discussing, you did not state that. Even if that is what you were discussing, there are no collisions between the body and the arms in your device.

The word is PULL. Why do you keep misquoting?
I am not misquoting, because I am not quoting you. I am independently describing things using the correct words.

You keep saying that you are moving something away from you by pulling it, but as I stated in a previous post, by definition applying a force to move something away from you means pushing it. Pulling it would move it towards you.

http://www.dictionary.com/browse/push
http://www.dictionary.com/browse/pull

You also completely ignored the questions I asked in the previous post such as: Do you know what "center of mass" means?

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #94 on: 10/23/2017 02:12 PM »
So we can use potential energy with attraction forces to move an object without exhaust.

Sure you can... If the potential energy is with respect to something outside of your device like the gravitational attraction of a planet such as when doing an Oberth maneuver but not internally to your device.

I am in space and am holding the ends of a spring. I PULL on the spring and stretch the spring. The spring applies an equal and opposite force on each hand so I do not move. I let go of the spring. Please, please, tell me and everyone reading this thread that the spring when it is contracting does NOT apply a force on the hand that is holding the one end of the spring.

The force the spring applies to both hands when stretched disappears the instant one hand let's go. Any residual effects that happen due to potential energy stored in the spring and the muscles of both arms won't end up moving the center of mass of the system.

I asked will the contracting spring apply a force to the one hand?

The force exists before the spring is let go but not after. So, I believe no, the spring doesn't apply a force to the hand that remains holding it.

Let me answer the question in a more positive way. I know that the contracting spring will apply a force, so we have to refer to  second law. Look at the slinky experiment for proof.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #95 on: 10/23/2017 02:14 PM »
Then it's a two body problem, one hand and the spring and the hand that let go.

One hand and the spring will move one way <     > the other hand will move the other way

But the centre of mass of the combined system (both hands and the spring) will stay in the same place.

Ermmmmmmmmmmmmmmmmmmmmmmmmmmm............................. no.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #96 on: 10/23/2017 02:18 PM »
Live empirically!  No need to ask people what they think about this.  Build a model of the system you are thinking of.  It might be suspended above an air table or floating on still water.  Use a small radio-controlled actuator to release the end of the spring.  Run the experiment and report back to us. 

Well I like to say that physics is a science not a religion, so thinking is not a bad thing to do. Please refer to the slinky experiment in my earlier thread as reporting back to you.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #97 on: 10/23/2017 02:20 PM »
If you are not afraid of simple maths, try reading this, Collisions

Playing pool has never scared me.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #98 on: 10/23/2017 02:26 PM »
Are you saying that when the motor on the device is switched off the rotor arms do not collide with the body magnet?
What rotor arms? you didn't describe any rotor arms in your post, and if you are somehow referring to the device that you previously were discussing, you did not state that. Even if that is what you were discussing, there are no collisions between the body and the arms in your device.

The word is PULL. Why do you keep misquoting?
I am not misquoting, because I am not quoting you. I am independently describing things using the correct words.

You keep saying that you are moving something away from you by pulling it, but as I stated in a previous post, by definition applying a force to move something away from you means pushing it. Pulling it would move it towards you.

http://www.dictionary.com/browse/push
http://www.dictionary.com/browse/pull

You also completely ignored the questions I asked in the previous post such as: Do you know what "center of mass" means?

If I can offer some advice, if you find yourself stabbed in the stomach do not attempt to pull the knife from your body. And yes I do know what center of mass means, What do you know about about second law?

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #99 on: 10/23/2017 04:04 PM »
If I can offer some advice, if you find yourself stabbed in the stomach do not attempt to pull the knife from your body.
Pulling the knife into me would certainly be a stupid idea. Having someone else pull it out would be a good idea. Yes, people sometimes would say "pull it out" when talking about removing it from themselves (from the perspective of the hand which is on the other side of the knife from your body, this makes sense), which is why I did not make a big deal of you using the word pull. The definitions of the words push and pull have been more than adequately clarified and was never relevant, since the act of moving the magnet away from the other one has a clearly defined direction, so you should go back and read my description again with this understanding.

And yes I do know what center of mass means,
Then why have you ignored all statements related to it clarifying that the center of mass of a system with no external forces applied to it will not move?

What do you know about about second law?
I know that it says that the center of mass of a system will accelerate when external forces are applied to it, and that it will not accelerate if no external forces are applied to it. The situations you are describing do not include external forces.

Offline 192

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Re: Conservation of energy/momentum.
« Reply #100 on: 10/24/2017 02:50 PM »
Let your spring have mass M1, and the person have mass M2, and at the start let them be at position 0.

Then when you release the spring, the spring moves towards the hand holding it, and the body moves in the opposite direction.

If the spring is moving at speed v, then the person will be moving in the opposite direction by M1/M2 * v.

Their velocities will always be in these proportions.

So if when then the hand and spring collide and come to rest the spring is at position x, the person will have moved in the opposite direction by M1/M2 * x.

So the center of mass of the whole system will be positioned at M1 * x - M2 * (M1/M2 * x) = 0.

Offline nacnud

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Re: Conservation of energy/momentum.
« Reply #101 on: 10/24/2017 02:59 PM »
Then it's a two body problem, one hand and the spring and the hand that let go.

One hand and the spring will move one way <     > the other hand will move the other way

But the centre of mass of the combined system (both hands and the spring) will stay in the same place.

Ermmmmmmmmmmmmmmmmmmmmmmmmmmm............................. no.

Ermmmmm yes. Please stop with this nonsense.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #102 on: 10/24/2017 03:41 PM »
Let your spring have mass M1, and the person have mass M2, and at the start let them be at position 0.

Then when you release the spring, the spring moves towards the hand holding it, and the body moves in the opposite direction.

If the spring is moving at speed v, then the person will be moving in the opposite direction by M1/M2 * v.

Their velocities will always be in these proportions.

So if when then the hand and spring collide and come to rest the spring is at position x, the person will have moved in the opposite direction by M1/M2 * x.

So the center of mass of the whole system will be positioned at M1 * x - M2 * (M1/M2 * x) = 0.

Also the spring forces are internal, so I am external to the spring. If I am external to the spring, the spring is external to me. When the spring is stretched, third law applies. When I let go of the spring I move a piece on the chess board, nature must respond. The spring now applies an external force to me and I move.
If it is a requirement for the jigsaw piece to fit snugly into place with the pieces already laid, then the spring applies an exterior force to me for a short period of time.
If the question is "can you move an object without any exhaust" the answer is "yes".

Offline nacnud

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Re: Conservation of energy/momentum.
« Reply #103 on: 10/24/2017 03:49 PM »
When the spring is stretched, third law applies. When I let go of the spring... The spring now applies a external force to me and I move.

The spring and you are part of the same system. There are no external forces. The centre of mass of the system does not move.
« Last Edit: 10/24/2017 03:50 PM by nacnud »

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #104 on: 10/24/2017 04:15 PM »
When the spring is stretched, third law applies. When I let go of the spring... The spring now applies a external force to me and I move.

The spring and you are part of the same system. There are no external forces. The centre of mass of the system does not move.

Are you saying I do not move?

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #105 on: 10/24/2017 04:26 PM »
When the spring is stretched, third law applies. When I let go of the spring... The spring now applies a external force to me and I move.

The spring and you are part of the same system. There are no external forces. The centre of mass of the system does not move.

Are you saying I do not move?
Read his post again, particularly the part where he modified the quote of you to be correct.

The amount you move is limited by the amount the spring moves, and moving the spring back moves you back:
So if when then the hand and spring collide and come to rest the spring is at position x, the person will have moved in the opposite direction by M1/M2 * x.

Also the spring forces are internal, so I am external to the spring. If I am external to the spring, the spring is external to me. When the spring is stretched, third law applies. When I let go of the spring I move a piece on the chess board, nature must respond. The spring now applies an external force to me and I move.
If it is a requirement for the jigsaw piece to fit snugly into place with the pieces already laid, then the spring applies an exterior force to me for a short period of time.
If the question is "can you move an object without any exhaust" the answer is "yes".
If you insist on considering the spring as external to you, then the motion of the spring is your exhaust, so no, you are not moving without exhaust.

Offline nacnud

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Re: Conservation of energy/momentum.
« Reply #106 on: 10/24/2017 04:28 PM »
No, that the centre of mass of you plus the spring does not move.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #107 on: 10/24/2017 04:46 PM »
The amount you move is limited by the amount the spring moves, and moving the spring back moves you back:

The spring will apply equal and opposite again. If you are suggesting that I move when I move my arms then I can simply do the superman maneuver and go where I please.

If you insist on considering the spring as external to you, then the motion of the spring is your exhaust, so no, you are not moving without exhaust.

If that is all you have then I am making progress.

 No, that the centre of mass of you plus the spring does not move.

Does my position change?

Since we have established that I accelerate, which terminology do you prefer, exterior force or unbalanced force?


« Last Edit: 10/24/2017 05:02 PM by chazemz »

Offline whitelancer64

Re: Conservation of energy/momentum.
« Reply #108 on: 10/24/2017 05:13 PM »
The amount you move is limited by the amount the spring moves, and moving the spring back moves you back:

The spring will apply equal and opposite again. If you are suggesting that I move when I move my arms then I can simply do the superman maneuver and go where I please.

If you insist on considering the spring as external to you, then the motion of the spring is your exhaust, so no, you are not moving without exhaust.

If that is all you have then I am making progress.

 No, that the centre of mass of you plus the spring does not move.

Does my position change?

Since we have established that I accelerate, which terminology do you prefer, exterior force or unbalanced force?

No. You do not accelerate.

Moving your arm shifts a part of you around, but does not move your center of mass. All you are doing is redistributing your mass. Moving your arm back to its original position will return you to your original position.

Here is something you can do to understand this concept:

Take a pen and a ruler. Remove the cap from the pen so it rolls smoothly. Place the ruler on top of the pen. Imagine this is your spacecraft, with yourself and the springs inside it, and the pen is the center of mass. Shifting your body or the springs is like sliding the ruler to the left. Shifting yourself or the springs back to your original position is like sliding the ruler to the right. But no matter how you move, the spacecraft only shifts around the center of mass.
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Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #109 on: 10/24/2017 05:45 PM »
The amount you move is limited by the amount the spring moves, and moving the spring back moves you back:

The spring will apply equal and opposite again. If you are suggesting that I move when I move my arms then I can simply do the superman maneuver and go where I please.

If you insist on considering the spring as external to you, then the motion of the spring is your exhaust, so no, you are not moving without exhaust.

If that is all you have then I am making progress.

 No, that the centre of mass of you plus the spring does not move.

Does my position change?

Since we have established that I accelerate, which terminology do you prefer, exterior force or unbalanced force?

No. You do not accelerate.

Moving your arm shifts a part of you around, but does not move your center of mass. All you are doing is redistributing your mass. Moving your arm back to its original position will return you to your original position.

Here is something you can do to understand this concept:

Take a pen and a ruler. Remove the cap from the pen so it rolls smoothly. Place the ruler on top of the pen. Imagine this is your spacecraft, with yourself and the springs inside it, and the pen is the center of mass. Shifting your body or the springs is like sliding the ruler to the left. Shifting yourself or the springs back to your original position is like sliding the ruler to the right. But no matter how you move, the spacecraft only shifts around the center of mass.

Thank you for the reply. I am a little confused. If I am holding the spring in my left hand after it has contracted, does this refer to moving my right hand to my left hand. If so would not the opposite happen if I move my left hand, with spring, to my empty hand. What will happen If I move both hands together at the same time?

Offline whitelancer64

Re: Conservation of energy/momentum.
« Reply #110 on: 10/24/2017 06:02 PM »
The amount you move is limited by the amount the spring moves, and moving the spring back moves you back:

The spring will apply equal and opposite again. If you are suggesting that I move when I move my arms then I can simply do the superman maneuver and go where I please.

If you insist on considering the spring as external to you, then the motion of the spring is your exhaust, so no, you are not moving without exhaust.

If that is all you have then I am making progress.

 No, that the centre of mass of you plus the spring does not move.

Does my position change?

Since we have established that I accelerate, which terminology do you prefer, exterior force or unbalanced force?

No. You do not accelerate.

Moving your arm shifts a part of you around, but does not move your center of mass. All you are doing is redistributing your mass. Moving your arm back to its original position will return you to your original position.

Here is something you can do to understand this concept:

Take a pen and a ruler. Remove the cap from the pen so it rolls smoothly. Place the ruler on top of the pen. Imagine this is your spacecraft, with yourself and the springs inside it, and the pen is the center of mass. Shifting your body or the springs is like sliding the ruler to the left. Shifting yourself or the springs back to your original position is like sliding the ruler to the right. But no matter how you move, the spacecraft only shifts around the center of mass.

Thank you for the reply. I am a little confused. If I am holding the spring in my left hand after it has contracted, does this refer to moving my right hand to my left hand. If so would not the opposite happen if I move my left hand, with spring, to my empty hand. What will happen If I move both hands together at the same time?

Either way, you are still just shifting mass around. Which arm moves, or moving both, doesn't matter.

*edit* Maybe watching videos of astronauts on the ISS would help, too. Like this one,
« Last Edit: 10/24/2017 06:03 PM by whitelancer64 »
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
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Online meberbs

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Re: Conservation of energy/momentum.
« Reply #111 on: 10/24/2017 07:59 PM »
Please use quotes properly.

The spring will apply equal and opposite again.
Yes, the spring applying equal and opposite again is why moving the spring back to its original position will move you back to your original position.

If you are suggesting that I move when I move my arms then I can simply do the superman maneuver and go where I please.
I have no idea how you get from me saying that you are limited by how far the spring moves to thinking the superman maneuver lets you fly. That is as opposite to what I said as possible. If you are standing on a frictionless surface (or in space) moving your arm to the right will move the rest of your body slightly to the left, and moving your arm back restores you to the original position.

Quote from: meberbs
If you insist on considering the spring as external to you, then the motion of the spring is your exhaust, so no, you are not moving without exhaust.

If that is all you have then I am making progress.
You are only making progress if you understand what I said, and your response indicates that you don't.

Quote from: nacnud
No, that the centre of mass of you plus the spring does not move.
Does my position change?
You claimed that you understand the concept of center of mass, so why don't you answer your own question: Given that the center of mass does not move, and the position of the spring has changed, has your position changed?

Since we have established that I accelerate, which terminology do you prefer, exterior force or unbalanced force?
Since you are holding onto the spring it is simpler to consider the system of you plus the spring, rather than the spring and you separately. The preferred term is therefore internal force. The same applies to the system with you and the magnets, because while you may not be physically touching the magnet the whole time, you both start and end the scenario while touching the magnet.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #112 on: 10/25/2017 01:36 PM »
Some people seem to be getting confused by the spring. We will assume that my center of mass is the middle of my chest. With no spring attached move my arms away from my chest and then return them to their original position. Now consider what will happen when I do so.
Now attach the spring to the middle of my chest and stretch the spring, letting go, and returning my arms to the end of the spring.
Now consider what will happen. Since the spring has applied an unbalanced force to me, the result must be different.

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Re: Conservation of energy/momentum.
« Reply #113 on: 10/25/2017 04:18 PM »
Some people seem to be getting confused by the spring.
The only person here confused by the spring is you.

We will assume that my center of mass is the middle of my chest. With no spring attached move my arms away from my chest and then return them to their original position.Now consider what will happen when I do so.
Since you manage to find a way to misunderstand everything you have been told, I supplied an attached diagram. Your arms move one way, the rest of your body moves the other. The blue line represents the position of the center of mass relative to the horizontal axis. You return to your original position by returning your arms to your sides.

Now attach the spring to the middle of my chest and stretch the spring, letting go, and returning my arms to the end of the spring.
Now consider what will happen. Since the spring has applied an unbalanced force to me, the result must be different.
Net forces between you and the spring are no different than the net forces between your arms and the rest of your body. The exact same diagram I drew applies, except with the spring you are holding effectively making your arms more massive (but I had exaggerated the relative mass of arms in the diagram anyway for clarity.)

Breaking it up this way with your arms not being part of you seems weird, but works no different than you continuing to treat a spring that is attached to you as not part of the system.

Edit: Missed the attachment the first time.
« Last Edit: 10/25/2017 04:27 PM by meberbs »

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #114 on: 10/26/2017 03:12 PM »
Since you manage to find a way to misunderstand everything you have been told, I supplied an attached diagram. Your arms move one way, the rest of your body moves the other. The blue line represents the position of the center of mass relative to the horizontal axis. You return to your original position by returning your arms to your sides.


Just so I do not misunderstand you. You are saying that as I move my arms away from my body, my body moves away from my arms and when I move my arms towards my body , my body moves towards my arms. Is that correct?

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Re: Conservation of energy/momentum.
« Reply #115 on: 10/26/2017 03:43 PM »
Just so I do not misunderstand you. You are saying that as I move my arms away from my body, my body moves away from my arms and when I move my arms towards my body , my body moves towards my arms. Is that correct?
Correct, this is clearly necessary for your center of mass to remain in the same position, and for conservation of momentum.

Offline Bob012345

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Re: Conservation of energy/momentum.
« Reply #116 on: 10/26/2017 04:49 PM »
Just so I do not misunderstand you. You are saying that as I move my arms away from my body, my body moves away from my arms and when I move my arms towards my body , my body moves towards my arms. Is that correct?
Correct, this is clearly necessary for your center of mass to remain in the same position, and for conservation of momentum.

This is a rare case where if you cut your nose off to spite your face, you may actually get somewhere. :)

Offline Bob012345

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Re: Conservation of energy/momentum.
« Reply #117 on: 10/26/2017 06:19 PM »
Since you manage to find a way to misunderstand everything you have been told, I supplied an attached diagram. Your arms move one way, the rest of your body moves the other. The blue line represents the position of the center of mass relative to the horizontal axis. You return to your original position by returning your arms to your sides.


Just so I do not misunderstand you. You are saying that as I move my arms away from my body, my body moves away from my arms and when I move my arms towards my body , my body moves towards my arms. Is that correct?

Not exactly the same thing but a related concept is what happens when ice skaters spin up and down. In that case, the center of mass is also fixed but the Moment of Inertia changes as arms are pushed out or pulled in and the spin speed adjusts to conserve angular momentum. In this case, the center of mass is fixed but the distribution of mass changes when arms are pushed out or pulled in.

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Re: Conservation of energy/momentum.
« Reply #118 on: 10/26/2017 07:10 PM »
Just so I do not misunderstand you. You are saying that as I move my arms away from my body, my body moves away from my arms and when I move my arms towards my body , my body moves towards my arms. Is that correct?
That is absolutely correct. It is somewhat counter-intuitive, because it is at variance with our everyday experience.

When you stand on the ground and raise your arms out in front of you, you normally do not detect any movement of your body. That is because friction on the soles of your feet couple you to the planet and so the system that moves back is your body plus the planet. The planet is so much more massive than your arms that the movement is infinitesimal.

If you conducted the experiment on a frictionless surface (an air table or ice rink, say) or in space, the effect would be observable if you took care. Your arms account for about 10% of an average body mass, so if you raise your arms out in front of you, you move their centre of mass forward about a foot (half an arm's length). The centre of mass of the rest of your body will move back about one-ninth of that, i.e. just over one inch. The centre of mass of the combined system (arms plus body) won't move at all.

(Similarly, your body will move down as you raise your arms - again not observed in everyday experience, because of the forces exerted by the surface of the Earth supporting you)

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #119 on: 10/27/2017 09:21 AM »
Just so I do not misunderstand you. You are saying that as I move my arms away from my body, my body moves away from my arms and when I move my arms towards my body , my body moves towards my arms. Is that correct?
That is absolutely correct. It is somewhat counter-intuitive, because it is at variance with our everyday experience.

When you stand on the ground and raise your arms out in front of you, you normally do not detect any movement of your body. That is because friction on the soles of your feet couple you to the planet and so the system that moves back is your body plus the planet. The planet is so much more massive than your arms that the movement is infinitesimal.

If you conducted the experiment on a frictionless surface (an air table or ice rink, say) or in space, the effect would be observable if you took care. Your arms account for about 10% of an average body mass, so if you raise your arms out in front of you, you move their centre of mass forward about a foot (half an arm's length). The centre of mass of the rest of your body will move back about one-ninth of that, i.e. just over one inch. The centre of mass of the combined system (arms plus body) won't move at all.

(Similarly, your body will move down as you raise your arms - again not observed in everyday experience, because of the forces exerted by the surface of the Earth supporting you)


 We can now move to the spring. As I pull the spring away from me and stretch it, the spring will resist and apply a force against the movement of my arms and my body.
So does my body still move backwards (and if so by how much), applying a ever greater force on the spring and vice versa or is its movement hampered by the increasing potential energy of the spring?


Online meberbs

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Re: Conservation of energy/momentum.
« Reply #120 on: 10/27/2017 10:53 AM »
Just so I do not misunderstand you. You are saying that as I move my arms away from my body, my body moves away from my arms and when I move my arms towards my body , my body moves towards my arms. Is that correct?
That is absolutely correct. It is somewhat counter-intuitive, because it is at variance with our everyday experience.

When you stand on the ground and raise your arms out in front of you, you normally do not detect any movement of your body. That is because friction on the soles of your feet couple you to the planet and so the system that moves back is your body plus the planet. The planet is so much more massive than your arms that the movement is infinitesimal.

If you conducted the experiment on a frictionless surface (an air table or ice rink, say) or in space, the effect would be observable if you took care. Your arms account for about 10% of an average body mass, so if you raise your arms out in front of you, you move their centre of mass forward about a foot (half an arm's length). The centre of mass of the rest of your body will move back about one-ninth of that, i.e. just over one inch. The centre of mass of the combined system (arms plus body) won't move at all.

(Similarly, your body will move down as you raise your arms - again not observed in everyday experience, because of the forces exerted by the surface of the Earth supporting you)


 We can now move to the spring. As I pull the spring away from me and stretch it, the spring will resist and apply a force against the movement of my arms and my body.
So does my body still move backwards (and if so by how much), applying a ever greater force on the spring and vice versa or is its movement hampered by the increasing potential energy of the spring?
Your body will move backwards more. Now the mass of your arms plus the mass of the spring is extended forward, so your body moves backwards more to compensate. For simplicity, assuming the mass of the spring plus the mass of your arms equals 20% of the total mass, using the rest of the same numbers that Nick did means your body would move backwards a bit more than 2 inches.

One thing to keep in mind is that the forces between your hands and one end of the spring are equal and opposite. The forces between the other end of your spring and where it is attached to you are equal and opposite. There is no rule stating that the force on one end of the spring is equal and opposite to the force on the other end of the spring. In fact these have to be unequal at some point to accelerate the center of mass of the spring away from your chest.

Intro physics textbooks discussing systems including springs assume massless springs so that the spring itself does not have to be accelerated which is a very good approximation in many practical cases. If we assume the spring in this case is very light compared to your body, then we just get the same final result as without the spring.

Note that I did not need to mention energy in this description. It is irrelevant at this point and we can move on to discussing energy once it is not going to just add more confusion.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #121 on: 10/27/2017 03:51 PM »
Just so I do not misunderstand you. You are saying that as I move my arms away from my body, my body moves away from my arms and when I move my arms towards my body , my body moves towards my arms. Is that correct?
That is absolutely correct. It is somewhat counter-intuitive, because it is at variance with our everyday experience.

When you stand on the ground and raise your arms out in front of you, you normally do not detect any movement of your body. That is because friction on the soles of your feet couple you to the planet and so the system that moves back is your body plus the planet. The planet is so much more massive than your arms that the movement is infinitesimal.

If you conducted the experiment on a frictionless surface (an air table or ice rink, say) or in space, the effect would be observable if you took care. Your arms account for about 10% of an average body mass, so if you raise your arms out in front of you, you move their centre of mass forward about a foot (half an arm's length). The centre of mass of the rest of your body will move back about one-ninth of that, i.e. just over one inch. The centre of mass of the combined system (arms plus body) won't move at all.

(Similarly, your body will move down as you raise your arms - again not observed in everyday experience, because of the forces exerted by the surface of the Earth supporting you)


 We can now move to the spring. As I pull the spring away from me and stretch it, the spring will resist and apply a force against the movement of my arms and my body.
So does my body still move backwards (and if so by how much), applying a ever greater force on the spring and vice versa or is its movement hampered by the increasing potential energy of the spring?
Your body will move backwards more. Now the mass of your arms plus the mass of the spring is extended forward, so your body moves backwards more to compensate. For simplicity, assuming the mass of the spring plus the mass of your arms equals 20% of the total mass, using the rest of the same numbers that Nick did means your body would move backwards a bit more than 2 inches.

One thing to keep in mind is that the forces between your hands and one end of the spring are equal and opposite. The forces between the other end of your spring and where it is attached to you are equal and opposite. There is no rule stating that the force on one end of the spring is equal and opposite to the force on the other end of the spring. In fact these have to be unequal at some point to accelerate the center of mass of the spring away from your chest.

Intro physics textbooks discussing systems including springs assume massless springs so that the spring itself does not have to be accelerated which is a very good approximation in many practical cases. If we assume the spring in this case is very light compared to your body, then we just get the same final result as without the spring.

Note that I did not need to mention energy in this description. It is irrelevant at this point and we can move on to discussing energy once it is not going to just add more confusion.

So, I hold my body in position as I extend my arms. If I free my body and bring my arms toward me I can transfer the momentum of my body onto another object without the need for me push against anything?
I am going to push against the object.

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #122 on: 10/27/2017 04:11 PM »
So, I hold my body in position as I extend my arms.
How do you intend to hold your body in position?

There is no way to truly do so, except by moving something else in the direction your body would have moved.

If I free my body and bring my arms toward me I can transfer the momentum of my body onto another object without the need for me push against anything?
It is unclear what you are trying to say here. Starting from a position with your arms extended and you at rest, pulling your arms towards you will result in your body moving forward slightly ending up stationary with your arms near to your body as we previously discussed. Nothing else happens unless you hit something while making that motion.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #123 on: 10/28/2017 09:09 AM »
So, I hold my body in position as I extend my arms.
How do you intend to hold your body in position?

There is no way to truly do so, except by moving something else in the direction your body would have moved.

If I free my body and bring my arms toward me I can transfer the momentum of my body onto another object without the need for me push against anything?
It is unclear what you are trying to say here. Starting from a position with your arms extended and you at rest, pulling your arms towards you will result in your body moving forward slightly ending up stationary with your arms near to your body as we previously discussed. Nothing else happens unless you hit something while making that motion.

Substitute my body for the body of the device (stator). Substitute my arms for the field flux lines and read the description again.
 It would be a good idea to add another magnet onto the belt in the collision scenario of the two counter rotating motors. You are correct read belt instead of body.

Offline Nick

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Re: Conservation of energy/momentum.
« Reply #124 on: 10/28/2017 01:41 PM »
So, I hold my body in position as I extend my arms. If I free my body and bring my arms toward me I can transfer the momentum of my body onto another object without the need for me push against anything?
Yes, of course you can. If you hit another object while your body is in motion (returning to its original position) that second object will, in general, move off in some direction, and your body will not return to rest in its original position. You will have  moved the second object but your body will also have moved from its original position and state of rest.

What you have described is effectively a complicated way of throwing the second object. Instead of simply holding it and throwing it away, you will have to position the second object so that part of you can collide with it while you move your arms.

All of these situations obey Newton's second & third laws. The second, F=ma, requires an external force in order to accelerate a body. The third, that every action has an equal and opposite reaction, means that when you add up the forces between all the components of a complex body (arms, legs, torso, stators, springs, magnets, nearby tennis balls, whatever) there is no net force on that total complex body as a whole. And hence no acceleration. It doesn't matter whether the forces between the individual components are provided by muscular contractions, springs, mechanical devices, chemical explosions, or by magnetic, electric or gravitational fields. The net total of all those forces is zero, and hence there can be no acceleration of the set of components in total. That doesn't mean than you can't move one component away from the others - but the centre of mass of the ejected component and those left behind doesn't move.

Exactly the same is true of a rocket. If a rocket is fired in empty space, the vehicle moves off in some direction, and the exhaust in the opposite direction. What  we don't usually think about is that, as the exhaust hurtles away from the vehicle, the centre of mass of the vehicle plus exhaust, taken together, doesn't move at all. As the 100+ tons of the Apollo/SIVB combination set off for the Moon, a similar quantity of propellant was sent in the opposite direction to whatever fate awaited it in later interactions with Earth & Sun.

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #125 on: 10/28/2017 03:40 PM »
So, I hold my body in position as I extend my arms.
How do you intend to hold your body in position?

There is no way to truly do so, except by moving something else in the direction your body would have moved.

If I free my body and bring my arms toward me I can transfer the momentum of my body onto another object without the need for me push against anything?
It is unclear what you are trying to say here. Starting from a position with your arms extended and you at rest, pulling your arms towards you will result in your body moving forward slightly ending up stationary with your arms near to your body as we previously discussed. Nothing else happens unless you hit something while making that motion.

Substitute my body for the body of the device (stator). Substitute my arms for the field flux lines and read the description again.
 It would be a good idea to add another magnet onto the belt in the collision scenario of the two counter rotating motors. You are correct read belt instead of body.
I cannot make those substitutions, because they don't make sense.  At a basic level a magnetic field does not have mass, while your arms do. Trying to make an analogy there is flawed. There also isn't an equivalent to extending your arms when it comes to magnetic fields.

Also, you seem to be switching from a linear motion system to a rotating one.

You also have to explain what you mean by "hold the body still"

You talk a bout a "device" and "collisions" The device you have shown a video of does not even come close to matching your description here (to start with it only has one motor) and the device you previously attempted to describe involving belts and magnets did not seem to be set up in such a way that a collision could occur. I'd ask for a better description, but most of your descriptions seem to assume that the person on the other end is psychic, so I will have to ask for a detailed labelled diagram.

Before moving on to this new system, it would be helpful if you acknowledged the previous description that when stretching a spring attached to you by extending your arms, the spring does not change the result other than increasing the mass of what you extend forward to be mass of arms plus string rather than mass of arms.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #126 on: 10/29/2017 08:50 AM »
So, I hold my body in position as I extend my arms.
How do you intend to hold your body in position?

There is no way to truly do so, except by moving something else in the direction your body would have moved.

If I free my body and bring my arms toward me I can transfer the momentum of my body onto another object without the need for me push against anything?
It is unclear what you are trying to say here. Starting from a position with your arms extended and you at rest, pulling your arms towards you will result in your body moving forward slightly ending up stationary with your arms near to your body as we previously discussed. Nothing else happens unless you hit something while making that motion.

Substitute my body for the body of the device (stator). Substitute my arms for the field flux lines and read the description again.
 It would be a good idea to add another magnet onto the belt in the collision scenario of the two counter rotating motors. You are correct read belt instead of body.
I cannot make those substitutions, because they don't make sense.  At a basic level a magnetic field does not have mass, while your arms do. Trying to make an analogy there is flawed. There also isn't an equivalent to extending your arms when it comes to magnetic fields.

Also, you seem to be switching from a linear motion system to a rotating one.

You also have to explain what you mean by "hold the body still"

You talk a bout a "device" and "collisions" The device you have shown a video of does not even come close to matching your description here (to start with it only has one motor) and the device you previously attempted to describe involving belts and magnets did not seem to be set up in such a way that a collision could occur. I'd ask for a better description, but most of your descriptions seem to assume that the person on the other end is psychic, so I will have to ask for a detailed labelled diagram.

Before moving on to this new system, it would be helpful if you acknowledged the previous description that when stretching a spring attached to you by extending your arms, the spring does not change the result other than increasing the mass of what you extend forward to be mass of arms plus string rather than mass of arms.

You have completely missed the plot here. The spring discussion is neither here or there. To expend so much energy to stop, start, stop, start, a millimetre at a time is, in my opinion, about as useful as a chocolate teapot. The point is to use  the scenario and the comments made (thank you to everyone who commented) as a platform to hopefully make some meaningful progress.
If it is your desire for me to be in error may I point to my comments on substitutes. The spring should be substituted for the field flux lines ( potential energy) and my arms for the armature reaction for the device in the video.

On a completely different subject, using electromagnets in the two counter rotating motor, belt scenario,  both the collision and push back  instances look cautiously promising.

Online meberbs

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Re: Conservation of energy/momentum.
« Reply #127 on: 10/29/2017 03:31 PM »
You have completely missed the plot here. The spring discussion is neither here or there. To expend so much energy to stop, start, stop, start, a millimetre at a time is, in my opinion, about as useful as a chocolate teapot. The point is to use  the scenario and the comments made (thank you to everyone who commented) as a platform to hopefully make some meaningful progress.
Based on this comment, it sounds like you still think that you can have net motion in the scenario with the spring. If you still think this, you still do not understand that scenario, and there is no point in discussing more complicated scenarios with you.

If it is your desire for me to be in error
It is my desire for you to stop being in error.

On a completely different subject, using electromagnets in the two counter rotating motor, belt scenario,  both the collision and push back  instances look cautiously promising.
On that subject, I just stated in my precious post that you have failed to describe that situation in such a way where a collision could occur. If you want to discuss it, you are going to have to find a better way to describe what in the world you are talking about. (But first lets settle the matter of you understanding that you can move exactly nowhere in the spring scenario no matter how much effort you exert.)

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #128 on: 10/30/2017 11:50 AM »
Basic sketch attached, there are numerous variations that can be made ie change position of hull magnets, add more magnets to belts, add a braking zone per cycle etc, etc, etc.

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Re: Conservation of energy/momentum.
« Reply #129 on: 10/30/2017 03:10 PM »
Basic sketch attached, there are numerous variations that can be made ie change position of hull magnets, add more magnets to belts, add a braking zone per cycle etc, etc, etc.
Thank you, it is much more clear what you are talking about now.

I still have no idea what you mean by a "collision" though because that setup does not include anything that would collide with anything else.

Before we discuss this situation you still haven't answered an important question: Do you understand that the scenarios described with stretching a spring that is attached to you you cannot move anywhere at all no matter how much time or effort you put in?

Assuming the answer is yes, so that there is a point in moving on to the device with the belts, then you'll understand a request to add a block of wood with the same mass as the magnet to each belt on the farthest point of each belt from the magnet. This will keep everything balanced, so that we don't have to discuss the slight useless back and forth of the hull that would otherwise be needed to balance momentum when both magnets on the belts are moving in the same direction.

Besides that, your setup does absolutely nothing interesting whatsoever and will not cause the hull of the ship to budge a single inch, doesn't even matter what orientation the magnets are in. An explanation of why you think otherwise would help in figuring out what exactly it is that you still don't understand.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #130 on: 10/30/2017 04:03 PM »
The belt magnets and the hull magnets are repelling each other so we will have the facing poles as north. I will go through some scenarios soon, mostly with electromagnets and hopefully someone will have some constructive comments. 

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Re: Conservation of energy/momentum.
« Reply #131 on: 10/30/2017 06:31 PM »
Last chance, if you have any interest in having a productive conversation, you need to answer this question. If you continue to ignore it and insist on moving on to another situation with more moving parts without demonstrating that you actually understand the conclusion from the previous discussion, no one is going to have any interest in continuing to converse with you.

Before we discuss this situation you still haven't answered an important question: Do you understand that in the scenarios described with stretching a spring that is attached to you, you cannot move anywhere at all no matter how much time or effort you put in?

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #132 on: 10/31/2017 11:00 AM »
The device is enclosed in the box (see diagram) and as I stated earlier, we will add another magnet of the same mass to each belt (all the magnets are electromagnets which at the start are all switched off). The additional magnets will be positioned so that when the motors are switched on, the box will not move. So we switch the motors on and the belts begin to move. When two of the belt magnets are approaching the hull magnets we can switch off the motors and switch on the belt and hull electromagnets. The belt magnets are now able to free wheel towards the hull magnets and since the magnetic orientation is repelling, they collide with the repelling magnetic fields imparting their momentum onto the hull magnets causing the body to move. We do not have to concern ourselves with the slight bounce back. Other configurations ie pull and push back can be considered.

Offline Basto

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Re: Conservation of energy/momentum.
« Reply #133 on: 10/31/2017 02:53 PM »
Your belt magnets are part of the same system as the hull magnets. No motion would occur as the belt magnets would push back with an equal amount of force as the hull magnets.

It’s the same reason you cannot lift a manhole cover you are standing on.

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #134 on: 10/31/2017 03:05 PM »
Your belt magnets are part of the same system as the hull magnets. No motion would occur as the belt magnets would push back with an equal amount of force as the hull magnets.

It’s the same reason you cannot lift a manhole cover you are standing on.


Remember, the belt magnets are moving and the hull magnets are stationary before the collision occurs.

Offline whitelancer64

Re: Conservation of energy/momentum.
« Reply #135 on: 10/31/2017 03:39 PM »
Your belt magnets are part of the same system as the hull magnets. No motion would occur as the belt magnets would push back with an equal amount of force as the hull magnets.

It’s the same reason you cannot lift a manhole cover you are standing on.


Remember, the belt magnets are moving and the hull magnets are stationary before the collision occurs.

It doesn't matter that you've made a set of magnets move and have another set fixed to the wall, it's still just the system pushing against itself. If you measure all the forces in the system they will turn out to be balanced. It's the same error you made with the spring, just with magnets this time. Moving the spring simply shifted the mass in the system around without it actually moving anywhere. The same thing happens with the magnets.

If you're not convinced, then maybe you should actually build this electromagnet contraption you've sketched out. Put it in a small cart with well-lubricated wheels, set it on a level, smooth floor, turn it on, see if it moves. Watch as it just rocks back and forth a bit without going anywhere.
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Offline Bob012345

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Re: Conservation of energy/momentum.
« Reply #136 on: 10/31/2017 03:41 PM »
Your belt magnets are part of the same system as the hull magnets. No motion would occur as the belt magnets would push back with an equal amount of force as the hull magnets.

It’s the same reason you cannot lift a manhole cover you are standing on.

We'll, actually you can in principle but probably impossible in practice..... same as skateboarders lifting the board they ride on. But only because both can react against the earth but the principle behind what I think you meant is correct.  :)

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #137 on: 10/31/2017 04:10 PM »
Your belt magnets are part of the same system as the hull magnets. No motion would occur as the belt magnets would push back with an equal amount of force as the hull magnets.

It’s the same reason you cannot lift a manhole cover you are standing on.

We'll, actually you can in principle but probably impossible in practice..... same as skateboarders lifting the board they ride on. But only because both can react against the earth but the principle behind what I think you meant is correct.  :)

When you turn the motors off, nature is in check. It only has one square to move and that is to transfer the momentum to the body.

Offline Bob012345

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Re: Conservation of energy/momentum.
« Reply #138 on: 10/31/2017 04:25 PM »
Your belt magnets are part of the same system as the hull magnets. No motion would occur as the belt magnets would push back with an equal amount of force as the hull magnets.

It’s the same reason you cannot lift a manhole cover you are standing on.

We'll, actually you can in principle but probably impossible in practice..... same as skateboarders lifting the board they ride on. But only because both can react against the earth but the principle behind what I think you meant is correct.  :)

When you turn the motors off, nature is in check. It only has one square to move and that is to transfer the momentum to the body.

My comment only concerned the manhole illustration. Your system has nothing to react against.
« Last Edit: 10/31/2017 04:27 PM by Bob012345 »

Online hop

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Re: Conservation of energy/momentum.
« Reply #139 on: 10/31/2017 04:35 PM »
The belt magnets and the hull magnets are repelling each other so we will have the facing poles as north. I will go through some scenarios soon, mostly with electromagnets and hopefully someone will have some constructive comments. 
Rather than coming up with more complicated contraptions, you would be far better served by taking the time to understand why your previous ideas were wrong. Once you do, you should realize why adding more springs/magnets/belts etc cannot change the basic outcomes, which will save you a lot of time and effort in the long run.

As others have suggested, a introductory physics course might help. You might also benefit from spending some time on https://www.lhup.edu/~dsimanek/museum/unwork.htm (spoiler: none of these devices do anything interesting)

Nothing you have posted here is "New Physics" (the subject of the forum) or has any novel or interesting implications concerning "Conservation of energy/momentum"

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #140 on: 10/31/2017 04:48 PM »
The belt magnets and the hull magnets are repelling each other so we will have the facing poles as north. I will go through some scenarios soon, mostly with electromagnets and hopefully someone will have some constructive comments. 
Rather than coming up with more complicated contraptions, you would be far better served by taking the time to understand why your previous ideas were wrong. Once you do, you should realize why adding more springs/magnets/belts etc cannot change the basic outcomes, which will save you a lot of time and effort in the long run.

As others have suggested, a introductory physics course might help. You might also benefit from spending some time on https://www.lhup.edu/~dsimanek/museum/unwork.htm (spoiler: none of these devices do anything interesting)

Nothing you have posted here is "New Physics" (the subject of the forum) or has any novel or interesting implications concerning "Conservation of energy/momentum"

I am more than happy for you to explain to me where the momentum goes?

Offline whitelancer64

Re: Conservation of energy/momentum.
« Reply #141 on: 10/31/2017 05:03 PM »
The belt magnets and the hull magnets are repelling each other so we will have the facing poles as north. I will go through some scenarios soon, mostly with electromagnets and hopefully someone will have some constructive comments. 
Rather than coming up with more complicated contraptions, you would be far better served by taking the time to understand why your previous ideas were wrong. Once you do, you should realize why adding more springs/magnets/belts etc cannot change the basic outcomes, which will save you a lot of time and effort in the long run.

As others have suggested, a introductory physics course might help. You might also benefit from spending some time on https://www.lhup.edu/~dsimanek/museum/unwork.htm (spoiler: none of these devices do anything interesting)

Nothing you have posted here is "New Physics" (the subject of the forum) or has any novel or interesting implications concerning "Conservation of energy/momentum"

I am more than happy for you to explain to me where the momentum goes?

Assuming you're talking about the magnetic fields, it gets cancelled out by the permanent magnets fixed on the hull. Your magnets are only pushing against each other. The forces involved are balanced, so your spaceship does not travel anywhere.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
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Online hop

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Re: Conservation of energy/momentum.
« Reply #142 on: 10/31/2017 05:04 PM »
I am more than happy for you to explain to me where the momentum goes?
https://www.lhup.edu/~dsimanek/museum/phys101.htm

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #143 on: 10/31/2017 05:22 PM »
The belt magnets and the hull magnets are repelling each other so we will have the facing poles as north. I will go through some scenarios soon, mostly with electromagnets and hopefully someone will have some constructive comments. 
Rather than coming up with more complicated contraptions, you would be far better served by taking the time to understand why your previous ideas were wrong. Once you do, you should realize why adding more springs/magnets/belts etc cannot change the basic outcomes, which will save you a lot of time and effort in the long run.

As others have suggested, a introductory physics course might help. You might also benefit from spending some time on https://www.lhup.edu/~dsimanek/museum/unwork.htm (spoiler: none of these devices do anything interesting)

Nothing you have posted here is "New Physics" (the subject of the forum) or has any novel or interesting implications concerning "Conservation of energy/momentum"

I am more than happy for you to explain to me where the momentum goes?

Assuming you're talking about the magnetic fields, it gets cancelled out by the permanent magnets fixed on the hull. Your magnets are only pushing against each other. The forces involved are balanced, so your spaceship does not travel anywhere.

You need to stop and think. Your problem is not that it works, but if it does not work. The alternative to it not working is to break most laws of physics. When you turn the motors off you decouple the armature from the stator so breaking the normal escape route. You are right in the magnets pushing against each other (they are electromagnets by the way) but the belt magnets have momentum (see collisions), that momentum must go somewhere and we have set up TINA (there is no alternative). As I have said before, if you are going to start the insults at least back them up with some facts. Nailing your feet to the floor and announcing to me that walking is impossible, as I walk past you makes no sense.

Offline whitelancer64

Re: Conservation of energy/momentum.
« Reply #144 on: 10/31/2017 06:00 PM »
The belt magnets and the hull magnets are repelling each other so we will have the facing poles as north. I will go through some scenarios soon, mostly with electromagnets and hopefully someone will have some constructive comments. 
Rather than coming up with more complicated contraptions, you would be far better served by taking the time to understand why your previous ideas were wrong. Once you do, you should realize why adding more springs/magnets/belts etc cannot change the basic outcomes, which will save you a lot of time and effort in the long run.

As others have suggested, a introductory physics course might help. You might also benefit from spending some time on https://www.lhup.edu/~dsimanek/museum/unwork.htm (spoiler: none of these devices do anything interesting)

Nothing you have posted here is "New Physics" (the subject of the forum) or has any novel or interesting implications concerning "Conservation of energy/momentum"

I am more than happy for you to explain to me where the momentum goes?

Assuming you're talking about the magnetic fields, it gets cancelled out by the permanent magnets fixed on the hull. Your magnets are only pushing against each other. The forces involved are balanced, so your spaceship does not travel anywhere.

You need to stop and think. Your problem is not that it works, but if it does not work. The alternative to it not working is to break most laws of physics. When you turn the motors off you decouple the armature from the stator so breaking the normal escape route. You are right in the magnets pushing against each other (they are electromagnets by the way) but the belt magnets have momentum (see collisions), that momentum must go somewhere and we have set up TINA (there is no alternative). As I have said before, if you are going to start the insults at least back them up with some facts. Nailing your feet to the floor and announcing to me that walking is impossible, as I walk past you makes no sense.

But it doesn't work.

None of the laws of physics are in any danger of being broken.

The electromagnets don't transfer any unbalanced momentum when they are switched off because you have a counter-balancing mass on the other side of the belt the electromagnet is fixed to. Even if you didn't, the transfer of momentum would simply reverse once the mass of the electromagnet travels around on the other side of the belt.

You seem to have a hard time understanding this.

I haven't insulted you, and in fact, I don't see where anyone else has insulted you anywhere here in this thread. Informing you that you are wrong in your understanding of physics and that your devices don't do anything interesting is not an insult, it's factual information.
« Last Edit: 10/31/2017 06:01 PM by whitelancer64 »
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline chazemz

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Re: Conservation of energy/momentum.
« Reply #145 on: 10/31/2017 06:27 PM »
The device is enclosed in the box (see diagram) and as I stated earlier, we will add another magnet of the same mass to each belt (all the magnets are electromagnets which at the start are all switched off). The additional magnets will be positioned so that when the motors are switched on, the box will not move. So we switch the motors on and the belts begin to move. When two of the belt magnets are approaching the hull magnets we can switch off the motors and switch on the belt and hull electromagnets. The belt magnets are now able to free wheel towards the hull magnets and since the magnetic orientation is repelling, they collide with the repelling magnetic fields imparting their momentum onto the hull magnets causing the body to move. We do not have to concern ourselves with the slight bounce back. Other configurations ie pull and push back can be considered.

May I suggest you read this again.

Offline Lar

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Re: Conservation of energy/momentum.
« Reply #146 on: 10/31/2017 07:03 PM »
perpetual motion machines are off topic. Locked.
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