Energy can be changed or converted from one form to another. But it is never destroyed or created, lost or gained. It is conserved – the amount stays the same. At the end of a process or event, the total amount of energy is the same as at the beginning. For example, the chemical energy in a car’s petrol is converted into the same amount of energy as the car’s motion, heat and sound. The principle of energy conservation means the total amount of energy in the Universe is always the same.

Another form of energy is matter itself. Matter can be converted into energy and energy can be changed into matter. This conversion is used in nuclear power stations. A nuclear particle called a neutron smashes into the nucleus of a uranium atom (1). The nucleus breaks into two parts (2). This releases large amounts of heat and other energy and also two more fast-moving neutrons (3). These smash into more uranium nuclei and so on in a chain reaction (4). Splitting of nuclei is known as nuclear fission. During the process bits of matter cease to exist and become vast quantities of energy instead.

A similar process of changing matter into energy happens naturally in the Sun. The Sun is made mainly of hydrogen. Tremendous temperatures and pressures at its centre squeeze or fuse together the nuclei of the atoms (1) to form the nucleus of a helium atom (2).Vast amounts of energy are given off (3) which emerge from the Sun mainly as light and heat. A neutron may also be given off to continue the reaction (4). Since the nuclei join or fuse, this is called nuclear fusion. Compared to fission used in our nuclear power stations, fusion power would cause less radioactive wastes and pollution. Fusion power may be the energy source of the future.

            Geothermal energy from hot rocks deep in the Earth causes geysers, jets of hot water and steam. This form of energy will last millions of years.

Picture Credit : Google