Energy is the ability to do work, such as the ability to move matter against opposing forces such as gravity and friction. Energy exists in several forms, including kinetic energy, which is the energy of motion, and potential energy, which is the capacity to do work.
Objects that possess energy because of their ability to move have kinetic energy. Potential energy is the energy of a body or system based on its position or arrangement of particles. According to
Dictionary.com, the most important property of energy is that it is conserved, which means that the total energy of an isolated system does not change with time. This property is known as the law of conservation of energy. Even though energy does not change with time, it does change form, such as when it turns into a mass and back into energy again.