Energy is present everywhere. Every subdivision of an atom present in a molecule of any matter or object possesses energy. Energy exists in various forms throughout the Universe.
There is thus a rule that governs the energy present in the Universe-
The Law of Conservation of Energy states that, “Energy can neither be created nor destroyed. It only changes from one form to another.”
This means that one form of energy is capable of turning itself into another form. Thus the net energy present in the Universe always remains constant.
For simplifying things, physicists define energy of a body as its capacity to do work.
Some important types of energy are-
• Potential Energy: The energy possessed by a body by virtue of its configuration or position is called potential energy. It is a kind of stored energy. When we stretch a spring or elastic, this type of energy is seen to be possessed by the spring. When we release the spring, this potential energy gets released and helps it to come back to its relaxed position. Potential energy also exists in objects kept at a height and is then called gravitational potential energy.
• Kinetic Energy: The energy possessed by a body by virtue of its state of motion is called kinetic energy. The energy possessed by a body moving in a straight line is called translational kinetic energy, possessed by a rotating body is called rotational kinetic energy and possessed by a vibrating body is called vibrational kinetic energy. Any moving object possesses kinetic energy. A shooting arrow or speeding train has kinetic energy.
• Mechanical Energy: When potential energy and kinetic energy take place together, one after another, it is called mechanical energy. Mechanical energy is also called the sum of potential and kinetic energy. A stretched spring has mechanical energy because its potential energy gets converted into kinetic energy which then helps the spring to recoil.
• Heat Energy: The energy released when something is burnt is called heat energy. For example, energy present in fuels, candles, burning wood, coal etc.
• Light Energy: Light is a very weak kind of energy. The radiation produced by light in the visible spectrum is called light energy. Light energy, though weak, can move dust particles. Thus, it has a capacity to do work. All luminous objects contain light energy. Eg. Light bulbs, sun rays etc. Light bulbs work by converting electrical and heat energy to light energy.
• Sound Energy: The energy possessed by a vibrating body is called sound energy. Sound energy does work by moving the molecules around us, so that the sound reaches our ears. For example, microphone, loudspeaker etc. are sources of sound energy. A microphone converts sound energy to electrical energy.
• Electrical Energy: The energy possessed by an electron that conducts electric current while moving through an electric wire is called electrical energy. It is important for modern living. All electrical appliances use electrical energy to work. Appliances like geysers and toasters convert electrical energy to heat energy while washing machines convert electrical energy to mechanical energy to do their work.
Besides these main forms of energy, a few other forms of energy harnessed by mankind are-
1. Energy generated from flowing water- hydroelectricity.
2. The energy possessed by a magnet- magnetic energy.
3. The energy generated by moving air- wind energy.
4. The energy possessed by fuels and chemicals- chemical energy.
5. Energy stored in hot water- thermal energy.
6. Energy stored in the nucleus of an atom- nuclear energy.