I've got a SAC which is my own experiment. The experiment is measure the Sag in a supported beam (A.K.A putting weights on top of a flexible ruler supported at both ends and measuring how much the ruler bent) Since i have to make referrence to law's and elaborate how the force affects the ruler, which of these following laws/methods should i make a mention of? - Hooke's law (Not sure) - Newton's third law (I think yes) - Elastic potential energy (?) here is a few pictures showing my experiment. Hopefully you can all grasp the visual concept of my experiment from these. http://img14.imageshack.us/img14/3015/variableweight.jpg [Broken] and another: http://img14.imageshack.us/img14/7941/variablelength.jpg [Broken] Anything else i should make mention of? any help would be greatly appreciated.