1. The problem statement, all variables and given/known data I don't know when the work of a spring is negative, and when it's positive... When is the work of a spring negative and when is it positive? 2. Relevant equations Wsp= -(1/2)(k)(xf2-xi2) 3. The attempt at a solution I can get Wsp to be positive when the spring is stretch, but I want to know the theory behind it.