Types of Energy

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

This is the law of conservation of energy, stated in the simplest form. It established two things - the sum total of energy in the universe is constant and energy manifests itself in various forms, that transform into each other. Every single event that occurs in this universe is an energy transformation of a particular kind. Through this Buzzle article, you will be introduced to the various types of energy.

Defining Energy

Almost every physical quantity can be precisely defined, except 'Energy'. Energy as a quantity, can only be indirectly observed and measured; the reason being the various forms in which it indirectly manifests itself. The enigmatic physical quantity called energy, can be roughly defined as the ability of any physical entity to do work, against exerted forces in the background. Therefore work and energy are very closely related. In fact, they have the same unit. We can further characterize energy through its observed properties which are - the fact that total energy of the universe always remains constant and it gets converted into various forms. Here is how the great physicist Richard Feynman explained the idea of energy -

"There is a fact, or if you wish, a law, governing all natural phenomena that are known to date. There is no known exception to this law-it is exact so far as we know. The law is called the conservation of energy. It states that there is a certain quantity, which we call energy, that does not change in manifold changes which nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says that there is a numerical quantity which does not change when something happens. It is not a description of a mechanism, or anything concrete; it is just a strange fact that we can calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same."

That 'number' which Feynman describes is Energy. Every natural phenomenon obeys the law of conservation of energy stated at the very beginning of this article. Energy is a scalar physical quantity, in the sense that it can be completely described by specifying its magnitude. In the International System of Units (SI), energy is measured in Joules. When energy manifests itself in the form of heat, it is measured using the unit of 'calorie' or 'Kilocalorie'. Everything that moves, jiggles, vibrates, rotates, causes motion to occur or has the potentiality to make things move, has energy. Let me introduce you to the various forms of energy in the rest of this write-up.

Different Forms of Energy

All the different types of energy can be broadly divided into two types - Potential and Kinetic Energy. The sum total of potential, as well as kinetic energy of a particle always remains constant, when there are no frictional forces operating. Let me define both of them, right away.

Potential Energy
The inherent, dormant energy stored in any physical system, due to its position and structure in an environment with applied forces is called potential energy. Picture an archer with a bow and arrow, ready to launch it. When the arrow is made ready for launch and the taut bowstring is pulled back, at that position, the string has elastic potential energy stored in it. In that position, the string has the 'potential' to perform the work to launch the arrow. There are various forms of potential energy, depending on the kind of forces involved. Examples are gravitational potential energy, chemical potential energy, electrical potential energy, magnetic potential energy and nuclear potential energy.

Kinetic Energy
Kinetic energy is the form of energy possessed by a particle due to its motion. In the above example, when the archer releases the bowstring, the arrow gets launched when the stored elastic potential energy gets converted into kinetic energy. The bowstring in motion possesses kinetic energy. Thus any particle in motion has kinetic energy. Examples are rotational kinetic energy and vibrational kinetic energy. The sum of potential and kinetic energies is known as mechanical energy.

Chemical Energy
The motive force that powers the human body, is provided by the chemical energy derived through the process of respiration. Chemical energy is derived from the making and breaking of inter-atomic bonds in molecules. Through molecular rearrangements, the biological world derives energy. The energy derived from gasoline is an example of chemical energy utilization.

Thermal Energy
Thermal or heat energy is the sum total of kinetic and potential energy of atoms and molecules that form a substance. Thermal energy can be measured by the temperature of the system under consideration. It is the energy of a substance, due to the vibrational, rotational and translational motion and potential energy of atoms and molecules.

Electric Energy
This is the energy derived from the electrical potential energy that exists between charges, which is delivered in the form of an electric current. When you connect the terminals of a battery with a bulb, electrical energy flows between the two terminals, in the form of the electric current, which are actually electrons traveling through the wire.

Elastic Energy
When you stretch a rubber band and then release it, the interatomic forces make it snap back to its original condition. The stored elastic potential energy is converted into kinetic energy to create the reversible motion which brings the elastic band to its original position.

Nuclear Energy
The energy derived from the conversion of a fractional nuclear mass into energy is nuclear energy. Defined by the celebrated Einsteinian equation - 'E=mc²' (where E is energy, m is lost mass and c is the speed of light), this energy is derived by inducing nuclear fission in certain radioactive isotopes like Uranium.

Sound Energy
Every sound that you hear, is the result of compression and rarefaction waves produced in air as a medium. Thus sound energy is derived from the oscillatory motion of air molecules.

Radiant Energy
The energy transported by electromagnetic waves is radiant energy. The light received from the Sun is an example of radiant energy. The spectrum of electromagnetic radiation is vast, from millimeter length waves to the high frequency gamma ray wavelengths. The energy transported through any such electromagnetic wave, be it from the radio, visible or X-ray bands, is directly proportional to its frequency.

Every single change that you see happening around you, is some kind of an energy transformation. To study physics, is to understand the various mechanisms behind these energy transformations. The different forms of energy listed above are only some of the most important ones. There are as many types of energy, as there are phenomena in nature.