On 12 Oct, 13:48, Rick Cavallaro wrote:
On Oct 12, 1:42*am, Thomas Prufer wrote:



Ah, ok, you're thinking the Earth vanishes, and the planets and stuff are still
around. I was thinking of a hollow shell of gas in a theoretical void -- the
same void used for electrons next an infinite plane with a charge... In such a
void, I'd think it would pull itself into a cloud without a hole in the middle,
slowly.

I'm pretty sure the cloud would not coalesce. *Each molecule of the
cloud has a velocity. *And that velocity will be greater than the
escape velocity for a body with the gravitational field of that cloud
itself. *This is why the moon has no atmosphere - and it has far more
gravitational pull than the cloud we're describing would.

An engineer friend saw a perpetual motion machine once...

Are you sure? *: )

The nearest thing I saw to perpetual motion was a little turbine in a
glass bulb that just rotated. It was suspended on a diamond resting
on a needle, ie very low friction. It was actuallypowered by light.
The turbine blades were shiny on one side and black on the other.
There was a vacuum in the glass bulb

Just a minute. The moon is in perptual motion round the Earth. Or as
near as dammit.