Re: [MLUG - DISCUSSION] Perpetual Motion Machine?

[Stephen Montgomery-Smith <EMAIL:PROTECTED>]

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

Gravity isn't really an energy source.  It is a way of storing energy. 
If you lift an object high up, it has more energy than when it is low 
down.  (This is called potential energy.)

For example, the heat from the sun evaporates water in the sea, and 
causes it to rise.  In this way, energy is stored.  Later this water 
falls as rain onto mountains, which then releases its energy by going 
downhill in rivers.  We can capture this released energy by building 
hyodrelectric plants that convert it to electricity (an amazingly 
transportable form of energy that even a few hundred years ago must have 
seemed impossible).

Thus, think of gravity as being a giant rechargable battery, that stores 
energy, but is not capable of producing it.


--

Stephen Montgomery-Smith
EMAIL:PROTECTED
http://www.math.missouri.edu/~stephen

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