# Perpetual Motion From Satellite Revolution

1. Jan 29, 2014

### LotoSage

"Perpetual Motion" From Satellite Revolution

This is going to sound very far fetched, and I know very little about the laws of physics, admittedly (I don't even know if I'm posting this in the right area), but curiosity compels me.

I was wondering if it would be possible to harvest energy from the revolution of a nearby satellite as I've illustrated here: http://i.imgur.com/Z3u5i33.png

I use the moon as an example here, but that could be replaced with any nearby satellite. Would this work, in theory?

2. Jan 30, 2014

### SteamKing

Staff Emeritus
I'm not sure what your sketch is trying to show. However, it is the policy at PF not to discuss PM and the like.

In any event, if you try to extract energy from an orbiting body, you are going cause that body to lose altitude over time. After all, it takes a fixed amount of energy per unit mass to put something into a particular orbit, so while your scheme may be long-lived, it cannot be 'perpetual'.

3. Jan 30, 2014

### LotoSage

Yeah, that's why I put it in quotes. While my understanding of physics is very limited I felt of course it couldn't last forever. I don't literally mean PM in this case (and that goes twicefold since it's disallowed), but simply a long term means of energy extraction. You seem to have gotten the right idea from my rudimentary illustration, and I thank you for your input.

4. Jan 30, 2014

### A.T.

We are already extracting that energy in practice:
http://en.wikipedia.org/wiki/Tidal_power‎

5. Jan 30, 2014

### Drakkith

Staff Emeritus
We'd have to expend more energy putting the satellites into orbit than we'd get back, so there's no point.

6. Jan 30, 2014

### sophiecentaur

It's all a matter of degree. The Moon is the largest object that will ever (could ever) be in orbit around the Earth. Any event that could introduce a comparable size of satellite would spell the end of the world for humans. Tidal surges or whaaaaat?

Tidal effects from the Moon (And the Sun, aamof) are many orders of magnitude greater than from anything else out there so those are the ones to go for. And we already do. From our point of view, the energy is 'inexhaustible' but it's not PM (verboten in PF).