the potential energy of a body which mass is "m" and which is moving in one demention is given by: U(x)=U0 * (a/x + x/a -2) what is the power which being put on the body the solution says F=-dU/dx=U0(-1/a + a/x^2) which means that they are doing a derivative to the original expression. but i cant understand why the derivative of potential energy is its power. from high school i know the potential energy is U=m*g*h and the only derivative that i know is for a(t)=v'(t) v(t)=x'(t) so their solution is not logic to me at all ???