A force is conservative if the work done by the force as the point of application moves around any closed path is zero. Consequently, the work done as the point of application moves from one point to another does not depend on the path taken, only on the end points. Gravity and the tension in a spring satisfying Hooke’s law are conservative forces. Only for a conservative force can potential energy be defined. More generally, a vector field is conservative if F = ∇φ‎ for a scalar field φ‎, called a potential, and hence curlF = 0. The work done ${\displaystyle {\int }_C^{}F\cdot \text{d}r}$, along an oriented curve C from a to b, then equals φ‎(b)–φ‎(a).