Re: how is elastic potential energy stored in a bow and arrow?

Think of the bow as being made up of a bunch of linked pieces.  Each of 
these pieces behaves like a spring, storing energy as one stretches it.  
Just like in a spring, the further you pull back on the bow, the more 
energy you store.

When the bow is in the "relaxed" state, there is no stored energy.  As you 
pull back on the bow, part of it (let's assume the inner wall) does not 
want to be compressed and so maintains it's relaxed length.  The only way 
the for the bow to be bent is if the outer wall stretches.  This stretching 
is storing the energy.

In a material, this stored energy is called "stress" and is measured as a 
force per unit area in the direction of the force.  In the US, it's common 
to measure it in pounds per square inch; the metric equivalent would be 
Newtons per square meter.

Christopher M. Seaman
Alcoa Technical Center