The 2 Main Forms of Energy

Although there are several types of energy, scientists can group them into two main categories: kinetic energy and potential energy. Here is a look at the forms of energy, with examples of each type.

Kinetic Energy

Kinetic energy is energy of motion. Atoms and their components are in motion, so all matter possesses kinetic energy. On a larger scale, any object in motion has kinetic energy.

A common formula for kinetic energy is for a moving mass:

KE = 1/2 mv²

KE is kinetic energy, m is mass, and v is velocity. A typical unit for kinetic energy is the joule.

Potential Energy

Potential energy is energy that matter gains from its arrangement or position. The object has the 'potential' to do work. Examples of potential energy include a sled at the top of a hill or a pendulum at the top of its swing.

One of the most common equations for potential energy can be used to determine the energy of an object with respect to its height above a base:

E = mgh

PE is potential energy, m is mass, g is acceleration due to gravity, and h is height. A common unit of potential energy is the joule (J). Because potential energy reflects the position of an object, it can have a negative sign. Whether it is positive or negative depends on whether work is done by the system or on the system.

Other Types of Energy

While classical mechanics classifies all energy as either kinetic or potential, there are other forms of energy.

Other forms of energy include:

• gravitational energy - the energy resulting from the attraction of two masses to each other.
• electric energy - energy from a static or moving electrical charge.
• magnetic energy - energy from the attraction of opposite magnetic fields, repulsion of like fields, or from an associated electric field.
• nuclear energy - energy from the strong force that bonds protons and neutrons in an atomic nucleus.
• thermal energy - also called heat, this is energy that can be measured as temperature. It reflects the kinetic energy of atoms and molecules.
• chemical energy - energy contained in chemical bonds between atoms and molecule.
• mechanical energy - the sum of the kinetic and potential energy.
• radiant energy - energy from electromagnetic radiation, including visible light and x-rays (for example).

 An object may possess both kinetic and potential energy. For example, a car driving down a mountain has kinetic energy from its movement and potential energy from its position relative to sea level. Energy can change from one form into others. For example, a lightning strike can convert electrical energy into light energy, thermal energy, and sound energy.

Conservation of Energy

While energy can change forms, it is conserved. In other words, the total energy of a system is a constant value. This is often written in terms of kinetic (KE) and potential energy (PE):

KE + PE = Constant

A swinging pendulum is an excellent example. As a pendulum swings, it has maximum potential energy at the top of the arc, yet zero kinetic energy. At the bottom of the arc, it has no potential energy, yet maximum kinetic energy.