# Question about energy and speed

1. Sep 13, 2004

### fizzzzzzzzzzzy

if we are moving at tousands of millions of miles per hour (rotation of universe) then souldn't we have burned up by now because of all the energy used to go that fast?

2. Sep 13, 2004

### daveed

rotation of the universe?
you mean the galaxy?
hows the universe rotate if its got nothing to compare against?

dont quite understand the question

3. Sep 13, 2004

### Gonzolo

Welcome fizzzzzzzzzzzzy!

Nowhere have I ever seen that the Universe rotates. I rather expands. I suspect you mean the galaxy.

But neither the spinning of the Earth, nor its displacement (around the Sun or galaxy) consumes any energy. If you're going 20 mph on a bicycle and you stop pedalling, the bike would go on forever (just like the Earth) if it weren't for friction between tire and road and friction in the wheel axles. There's no such friction in space to slow down the Earth.

4. Sep 16, 2004

### Grev

^ Somehow I find your answer isn't actually it... I'm not sure but I don't think our galaxies are perfectly isolated systems, so there would still be some sort of friction, right?

5. Sep 17, 2004

### Cyrus

There is no friction in outer space, only gravitational forces that can act on eachother over distances. Friction occurs between two objects in contact. Since space is a vaccume, there is no "contact" other than the forces that act over distances.

6. Sep 17, 2004

### HallsofIvy

"Moving fast" does not "require" energy. If we were suddenly to slow down, all the "kinetic energy" we have (which is what i think you are talking about) and if it were friction that was causing the slowing, it would go into heat. That is what cyrusabdollahi was talking about. Furthermore, all energy is relative to something else.
I you move a box of mass m up a height h, its potential energy is now mgh relative to its initial position. Our kinetic energy due to the "rotation of the universe" would be relative to the center of the universe (wherever that is) and is not particularly significant.

7. Sep 17, 2004

### geometer

According to general relativity, rotating, massive objects lose energy due to gravitomagnetic radiation. It's kind of the gravitational equivalent of the electromagnetic radiation emitted by accelerated charges. However, the rate of energy loss due to this gravitomagnetic radiation is incredibly small, so it's not a large immediate effect.

8. Sep 17, 2004

### Gonzolo

The only possible friction is cosmic rays, and collisions with dust, meteorites etc, which are negligeable as far as I know and can come from any direction quite symetrically.

Gravity and electromagnetic fields that could influence the course of something moving in space don't cause friction. They can accelerate it in any direction, but not stop it. There are conservative fields and non-conservative fields. Gravity and EM fields are conservative, friction is non-conservative.

9. Sep 17, 2004

### Everett

I disagree with the statement about EM fields not causing friction, or at least some force very much like it. Magnetic fields in space will induce eddy currents in conductors (plasmas, iron-nickel meteors, cores of planets) moving across the field lines. Creating eddy currents will slow down the conductor relative to the field lines. Unless these conductors have zero resistance (superconductor), then the eddy currents are dissipated as heat in the conductor. The overall effect is a retarding force on the conductor and the generation of heat. Seems alot like friction.

There are also friction arguments that could be made for time or position changing EM fields that act on matter, even nonconductors, via dielectric or diamagnetic effects.

Finally, since light is EM, and also carries momentum, and can be absorbed, matter colliding with photons experiences a force somewhat like friction. For very high velocities, an object will have hard hitting blue-shifted photons hitting it from the front while only wimpy red-shifted photons will hit it from the rear. This situation would imply some sort of velocity dependent retarding force on the object.

Last edited: Sep 17, 2004