# How is Energy Measured?

Energy is the ability to do work, where work is computed from the equation: Work = Force x Distance.

There is no absolute measure of energy, because energy definition is based on the work that one system does (or can do) on another. Thus, only the conversion of a system from one state into another can be tracked and thus measured.

Based on this definition, the standard unit of measurement of energy is the joule. One joule is one unit of work or energy required to be able to move an object with a force of one Newton across a distance of one meter. One Newton is measured from the force needed to move a mass of one kilogram over a distance of one meter in one second within a vacuum, and without friction.

The more familiar unit of measurement that we encounter is the watt. One watt (W) is equivalent to one joule of work per second. One kilowatt (kW) is equal to 1000 watts. The watt is the standard unit of electrical power. It is commonly used to describe the capacity of an electric generator, particularly small generating systems.

A calorie (cal), on the other hand, is the amount of heat needed to raise one gram of pure water from 14.5 to 15.5° Celsius under a condition of standard atmospheric pressure. One calorie is equal to 4.1855 joules. One kilocalorie (kcal) is equal to 1000 calories or 4185 joules.

## Forms of Energy

Energy occurs in various forms that are classified into two primary conditions: potential and kinetic.

Potential energy is static energy waiting to be released. The gasoline that runs our cars is an example.

Kinetic energy is the energy that a body possesses due to motion. A rock falling from a cliff has energy. You can feel this if it falls on your head. You can also feel the energy from the wind blowing through the air, which can move the leaves of a tree.

There are many other forms of energy. Some of them are enumerated below.

1. Radiant energy is emitted from a light source, such as the sun. The sun releases small particles of energy in the form of photons, which move in a manner similar to a wave. Solar panels convert the sun’s radiant energy to electrical energy.
2. Chemical energy is the energy produced or consumed in chemical reactions where the chemical bonds of a substance are destroyed, then rearranged into other molecules. An example is the conversion of food to energy for our metabolism through digestion.
3. Electrical energy is potential energy from electrons flowing along a circuit. Moving electrons create an electric current which can be transformed to another form of energy which we can use, like the light in our electric bulbs.