Why isn't torque-producing perpetual motion possible?

Question

I've read and re-read all the laws of motion and thermodynamics, blah blah blah. And yet, the earth and the universe keep spinning...

Of the 4 fundamental forces of nature, gravity is not understood. Given that we DON'T understand everything about our universe, how can it be said that it can't exist when our own earth is a prime example of torque-producing perpetual motion (angular momentum or whatever)?

Answer 1

The Earth's rotation is slowing down, very slowly, but still slowing down.

Answer 2

The earth is not an example of perpetual motion. The earth, sun and entire universe are very massive. All that mass was propelled by a whole lot of energy, and it's potential energy is being turned into kinetic energy as the earth falls slowly back toward the sun. All moving bodies in the universe will either fall back towards another moving body, or be slowed down by friction. There is not much in deep space to cause friction, so it's a slow process.

If we had the energy to manipulate something the mass of a star and an orbital body the mass of a planet, we might get the system orbiting, and might even be able to get some mechanical energy. It would probably last a long time.This system, like all closed systems will entropy in time. "A really long time" doesn't equate to perpetual.

At scales that would be necessary for it to be useful and feasible on earth, the system would slow and halt very, very quickly.

Answer 3

what torque, exactly, is produced by the earth?

Answer 4

the earth spinning produces no torque.

Answer 5

You don't understand what 'perpetual motion' means. First, it doesn't mean 'forever' - that's rather a long time.

It refers to a closed system, such as a machine, that is given an intitial charge of energy to get it started, but after that continues to operate by the feedback of part of its output to its input, and thus will operate until we turn it off or something wears out.

Obviousy, there will be losses due to friction, for example, so the system must amplify the energy it starts with to compensate and produce a surplus. Nobody has yet figured out a way to do that.

Answer 6

We also know that the earth is constantly slowing down.  over thousands of years our days have gotten longer, and will get longer still in the far distant future.

Our earth is NOT an example of perpetual motion.  It keeps spinning because there is very little energy being removed from the system.  but SOME energy IS being reomoved, and our rotation slows down.  And it will stop in a few million years, if the sun doesn't go nova first.