Energy

Energy is the ability to work. It comes in two basic forms: kinetic energy and potential energy. Kinetic energy is the energy of motion. For example the energy that a flying bullet has to crush the target object. Potential energy is the energy that an object has due to its position in a force field. For example, a book resting on a table has some stored energy which can produce sound when the book falls to the ground. This is a potential energy.

One of the most important laws of classical physics is the law of the conversation of energy.
This law states that energy can neither be created nor destroyed; rather, it transforms from one
form to another. For instance, chemical energy can transform into heat energy or potential
energy can transform into kinetic energy. This law was initially discovered in connection with
thermodynamics.