Elastic potential energy is the energy stored in a flexible object due to deformation caused by an external force. For example, when a bow is stretched, elastic potential energy is stored in the bow. Mathematically, it is defined as the product of force required to deform the object and displacement caused by the force. Thus, using Hooke’s law, the elastic potential energy of a bow stretched by a distance x can be expressed as 1/2 kx squared, where k is the spring constant. Lastly, consider a case where a body hangs from one end of a spring, which is fixed at the other end, as shown. The body exhibits both gravitational and elastic potential energy. Here, the total potential energy, U, is the sum of gravitational and elastic potential energy.