A concrete example I would very much like to see is something like this:
Take an acrylic ruler. it is 30 cm long, 3 cm wide and 2mm thick. It weighs 20grams (just estimated for this example).
Acrylic has Youngs Modulus of 3.2 GPa and ultimate Tensile Strength of 70 Mpa (according to the page I posted ealier).
If I took this material and used 500cm of it and turned it into a mainspring (or motor-spring), then:
a) What is the energy density of the spring?
b) If I didn't have Youngs Modulus and Ultimate Tensile Strength, how could I work these out (and any other values that I might need)?
Thanks and regards