Re: [MLUG - DISCUSSION] Perpetual Motion Machine?

[Mike Miller <EMAIL:PROTECTED>]

On Fri, 1 Sep 2006, Michael wrote:

> > Is there any energy source we humans use that doesn't come from the sun, 
> > at least indirectly?
>
> Gravity?

You can get energy from gravity if you raise an object away from the 
Earth's center of gravity.  But that merely stores the energy you expended 
in raising the object.  You can get the energy back if you can manage to 
extract *all* of the energy from the falling object.  But you cannot do 
this with perfect efficiency.  Therefore, you will lose some of the energy 
you expended in raising the object and gravity does not provide a good way 
of storing energy.

Hydroelectric power uses gravity.  The sun heats water so that it rises 
into the atmosphere and forms clouds which rain onto the land and onto 
fresh water that is above sea level.  The water is then moved by gravity 
back toward the ocean.  This gravitational energy can turn turbines or run 
mills.  It's a great energy source, but it depends on the sun to lift the 
water up in the first place.

Mike

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