Law of conservation of energy
What is it ?
The law of conservation of energy is a fundamental principle of physics which states that energy cannot be created or destroyed, only converted from one form to another or moved from one place to another. This means that the total energy of an isolated system remains constant over time.
When an object falls from a height, it acquires kinetic energy as it falls due to the force of gravity, on the other hand the potential energy related to its position decreases. The object's total energy remains constant, however, because the kinetic energy gained during the fall equals the potential energy lost.
When a car travels on a road, the energy in its tank in the form of fuel is converted into kinetic energy which drives the car forward and into the frictional energy of the air on the car. When the car brakes and stops, this kinetic energy is converted into heat, which is dissipated into the environment. The total energy of the car remains constant, however, because the energy produced by the fuel used to move the car is equal to the heat energy lost when stopping and air friction during travel.