Energy cannot be created or destroyed, only changed from one form to another.

James Prescott Joule helped prove this rule in 1843. He used a falling weight to spin a paddle in a container of water. The movement of the paddle made the water warmer. This showed that mechanical work turns into heat energy.In 1905, Albert Einstein added to this idea with his famous equation, E=mc². He proved that mass and energy are different versions of the same thing. In nuclear reactions, a small amount of matter turns into a large amount of energy. The total amount of mass and energy together does not change.This law means all the energy in the universe has existed since the Big Bang. This event happened about 13.8 billion years ago. Energy often changes into less useful forms, like heat. When a ball stops rolling, its energy does not vanish. Friction turns the movement into tiny amounts of heat in the ground and the air.