Because Fs varies as the object moves, the work done by or against the spring
cannot be written as Fd cosθ As with gravity, we must calculate work in terms of
potential energy. If a block on a spring moves from x 1 to x 2 , then
If an external force compresses or stretches the spring, then
Wagainst spring = +∆Us = k(x 22 − x 12 )