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?
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
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?
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.
Quote from: chazemz on 10/15/2017 11:21 amGoing 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.
Quote from: chazemz on 10/16/2017 07:14 pmThe 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.
Quote from: chazemz on 10/16/2017 11:34 amThere 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.
Quote from: ppnl on 10/15/2017 04:25 pmQuote from: chazemz on 10/15/2017 11:21 amGoing 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.
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.
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.
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.
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?
Quote from: chazemz on 10/18/2017 03:32 pmYou 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).
Quote from: meberbs on 10/18/2017 05:44 pmQuote from: chazemz on 10/18/2017 03:32 pmYou 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.
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?