Science Forums 2

[TeleMad]

I think we're all on the same page about the car idea, but just to make sure. Even if it did work and was more efficient energy wise, it still couldn't be a perpetual motion machine. The wheels would have to push against the ground to move the car and their contact with the ground would produce friction, which leads to frictional losses. You'd have to put energy into the system to maintain a constant angular velocity of the wheels, let alone produce an angular acceleration.

The real reason for brining this up is that it shows a general problem for perpetual motion machines. Mechanical machines the undergo a work cycle have parts that are in contact and that move relative to one another: this produces friction which results in a reduction in the system's mechanical energy. Thus, the system continues to lose energy, and, energy must be continually put into the system in order to keep it running. So if your idea has parts that are in contact and that move relative to one another, you might as well scrap it as far as being a perpetual motion machine is concerned.

As far as rotating magnets... Magnets have mass and we need to move them, which means we must apply a force to them. Applying a force to an object and having it move in response to that force is work. So we'd continue to do work on the magnet to keep it spinning. Energy is the ability to do work, and work and energy are equivalent. So we'd have to continue to put energy into the system to keep the magnets spinning. Thus, things with spinning magnets are not a perpectual motion machine candidate.

I should also point out that the real thing usually talked about is not perpetual motion, but rather a perpectual motion machine. Perpetual motion has already been achieved by nature. Photons released soon after the Big Bang have traveled for billions of years through space without any input of energy, and will continue to do so unless they run into something. The real trick is to try to get a work cycle out of a machine with the system having the same amount of available energy after the cycle as it did before the cycle, without adding any energy during the process.