Hi, Not sure if I'm asking this in the right place, but I was wondering about the energy stored in a rubber band for a physics project I am working on. We all know that for a spring or rubber band being extended, the restoring force is given by F=-kx, and the energy stored U=0.5kx2. However, I am considering using a rubber band to drive a propeller, in which case energy would be stored by twisting the band around many times. My question is, do you know of any way I could calculate the energy stored in the band in this way? Alternatively, a way to calculate the torque generated by the untwisting band would be very helpful to me too. I suspect it would depend on the constant k from the linear extension equation above, and also the length, width and thickness of the band as well as the number of turns, but I have not been able to come up with an expression myself or find one in my searches so far. Any links to sites that you think might help me, or textbooks, or anything else would be appreciated. Thanks.