I'd like to learn more about the way energy is stored in a springhttp://en.wikipedia.org/wiki/Spring_(device) . I found this site http://www.leespring.com/int_learn_compression.asp I learned that a 50mm free-length spring can be compressed for 20mm (at most by 40%) to solid length (30mm) and that 10% clash allowance must be left. So if the spring is compressed by 18 mm and the stiffness k is 12 N/mm the load is 18*12 216 N. Can you give me a good link where I can find the answers to the following questions? 1) how do I find the PE that can be stored in that spring when the load is 216N? what is the conversion formula? I found: .5*k*d^2 is the PE = K = .5*12*18^2 ? 2) supposing the positive work done to compress the spring is K J, how much of it can be actually stored, can we get values as high as 97-98%? 3) is the lost energy all transformed in heat, is the percentage linearly dependent on the mass?or on what? 4) if the stored energy is 97% K, will it be totally retrieved or some extra energy will be dispersed, and the actual energy restituted will be 94% K Lastly, if insead of a force applied there is an impulse, an impact with a body with KE,v and p, does anything change? can we find the released energy just applying the rate , say, 94%? Thanks for your help!