What is Energy?

By R.W. Hurst, Editor

What is Energy?

There are numerous forms of energy, but they can all be divided into two basic categories: Potential Energy and Kinetic Energy.

Potential energy: The best way to describe potential energy is that it is stored energy and the energy of position. For instance, an object can store energy as the result of its position. Think of the wrecking ball, part of a demolition machine, It is actually storing energy when it is held at an elevated position. This stored energy of position is referred to as potential energy. As soon as the ball is dropped, the potential energy is released.

Another example is a drawn bow. In this case, the bow is able to store energy as the result of its position. As soon as the arrow is fired, the potential energy of the bow is released. So, potential energy is defined as the stored energy of position possessed by an object.

Chemical energy refers to energy which is stored in the bonds of atoms and molecules. For instance, batteries, biomass, petroleum, natural gas, and coal are all good examples of chemical energy. The chemical energy, which is found in fossil fuels for instance, is converted into thermal energy when wood is burned in a fireplace or gasoline is burned in an automobile engine.

Mechanical energy refers to the energy which is stored in objects by tension. A good example of mechanical energy would be the compressed springs in your mattress or a stretched rubber band. Mechanical energy is the main driver of renewable energy. Many forms of renewable energy like wind and hydroelectric power rely on the mechanical energy of turbines to produce electric power. The physical motion of air or water over the blades, forces the blades to spin and the attached electrical generator also spins as a result, generating electricity.

Nuclear energy can be explained as energy which is stored in the nucleus of uranium atoms —which is the energy that binds the nucleus together. Large amounts of nuclear energy is released when the nuclei are combined (the “fusion” of hydrogen atoms, which is what happens in the sun) or split apart (“fission”), as in the case of a nuclear power reactor. In that case, uranium atoms are split, giving off thermal energy. This thermal energy is used to boil water on a large scale, which is then converted into high pressure steam, which in turn spins a turbine/generator to create electricity.

Gravitational energy is considered energy which is stored in an object's height. The higher and heavier the object, the more gravitational energy is stored. Hydroelectric power is a good example of gravitational energy. Gravity forces water to fall down through a hydroelectric tunnel where it falls onto spinning turbine blades, which in turn generate electricity.

Kinetic energy
Kinetic energy is best described as a form of energy that an object or a particle acquires by reason of its motion. If work, which transfers energy, is performed on an object by applying a net force, the object speeds up and thereby is said to gain “kinetic energy.”

Radiant energy is best described as: “electromagnetic energy that travels in transverse waves.” Examples of radiant energy include: visible light, x-rays, gamma rays, and radio waves. Light itself is one form of radiant energy. Sunlight is radiant energy, which provides both the fuel and warmth which makes life on Earth possible.

Thermal energy is energy contained in an object due to the movement of particles within the object. Think of a microwave oven and how it stimulates atoms, causing them to move. That motion causes the object to heat up. Because thermal energy is due to the movement of particles, it is a form of kinetic energy, which is defined as energy due to motion. 

Motion energy is said to be stored in the movement of objects. The faster they move, the more energy is stored. It takes energy to get a rocket launched into space, and the energy is released when the space capsule slows down upon reentry. 

Sound energy is defined as the movement of energy through a substance in longitudinal (compression/rarefaction) waves. In other words, sound energy is produced when a force causes an object or substance to vibrate. Think of a tuning fork. When the tuning fork is struck against an object, the energy is transferred through the fork in the form of a wave, and the result is the sound.

Electrical energy is delivered by tiny-charged particles called electrons, typically moving through a wire. Lightning is an example of electrical energy in nature.


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