The law of conservation of energy states that energy cannot be created nor destroyed, only transferred from one form to another. Energy can exist in different forms, such as thermal (heat), kinetic (movement) and potential (stored).
Not all energy is transferred to ‘useful’ forms of energy though – when you run, some of the chemical potential energy you use (from food) is ‘lost’ as heat and sound. According to some scientists, all energy and mass were created when the universe was born in the Big Bang nearly 14 billion years ago, and energy can be converted into mass (and vice versa).
