Anvil rebound,- horse poo? in Anvils, Swage Blocks, and Mandrels Posted October 6 Newton's third law . . . action / reaction. I think the college 101 physics class would use this law. If you sit in a chair, your body will exert force on the chair (from above),-and the chair will exert the same force on your body (from below). In our case, a piece of steel between a hammer and an anvil will be hit by two forces;-one from the hammer and one from the anvil according to Newton. If this has anything to do with anvil hardness,-I don't know. Let the 101 physics figure it out.