Answer
Energy is the capacity to do work. To do work means to move something, whether it is a muscle or a molecule. Potential energy is energy contained in an object because of its position or internal state but that is not doing work at the time. Kinetic energy is energy of motion, energy that is doing work. It is observed in musculoskeletal movements, the flow of ions into a cell, and vibration of the eardrum, for example.
Work Step by Step
Taken from Page 53 under "Energy and Work"
