. . "winsauceiswin (11/26/2012) [-] in general springs are described by -kx=ma where f=ma and therefore f=-kx where k is a constant describing the stiffness of the spring and x is the distance from which the spring compressed from equilibrium. the equation can be rearranged to be m=-kx/a where a is either the rate at which it is being compressed for is gravity. so you can see that the mass is technicall" . .