Opening doors, playing football, running a race – you really keep moving. What gives you the power to move?
The answer is energy! Your body gets its energy from food. The energy you get makes the pushes and pulls that keep you moving.
A car engine burns petrol. As the petrol burns, it gives off energy. That energy makes the pushes and pulls that turn the wheels.
There are many kinds of energy. Things that move, such as water and wind, have energy. Things that burn, such as fire, have energy. But the most important source of energy is the sun. It keeps everything on the earth on the move.
Energy, in physics, the capacity for doing work. It may exist in potential, kinetic, thermal, electrical, chemical, nuclear, or other various forms. There are, moreover, heat and work – i.e., energy in the process of transfer from one body to another. After it has been transferred, energy is always designated according to its nature. Hence, heat transferred may become thermal energy, while work done may manifest itself in the form of mechanical energy.
Energy can be neither created nor destroyed but only changed from one form to another. This principle is known as the conservation of energy or the first law of thermodynamics. For example, when a box slides down a hill, the potential energy that the box has from being located high up on the slope is converted to kinetic energy, energy of motion. As the box slows to a stop through friction, the kinetic energy from the box’s motion is converted to thermal energy that heats the box and the slope.
Energy can be converted from one form to another in various other ways. Usable mechanical or electrical energy is, for instance, produced by many kinds of devices, including fuel-burning heat engines, generators, batteries, fuel cells, and magneto-hydrodynamic systems.
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