measure for the ability of a system to do work

Energy can mean various things:

  • Mostly, it is used in science to describe how much potential a physical system has to change. In physics, energy is a property of matter and space, objects and fields. It can be transferred between objects and can also be converted in form. It cannot, however, be created or destroyed.
  • In economics it may mean the ‘energy industry,’ the harnessing and sale of energy itself as in fuel or electric power distribution.
  • In ordinary language, the word is used to describe someone acting or speaking in a lively and vigorous way.
  • It is a major part of physics and other sciences.
  • Energy can be used to heat, move or illuminate.

Scientific energyEdit

In physics, energy is the capacity to do work; the influence required to perform an action. The amount of energy in a system is the amount of change that can be made to it.

Basic forms of energy include:

  • Kinetic energy - energy of an object in motion, which acts as the capacity to undergo change in position over time.
  • Potential energy - stored energy, which acts as the potential to do work.
  • Heat - thermal energy which is used to vibrate atoms and molecules.
  • Electrical energy which is energy that relates to electrical interactions.

Conservation of EnergyEdit

Energy is a property that is not created or destroyed, although energy can change in detectable form.[1] This is a rule that is commonly understood as the "conservation law of energy". In respects to this rule, the total amount of energy that exists within an isolated system will always be the same, no matter what changes have been made to it.

In the early 20th century, scientist were able to discover that matter itself can be created from energy and vice versa. This is just another change of form. After these discoveries, the conservation law of energy was extended to become the conservation law of matter and energy: matter and energy can neither be created from nothing nor destroyed to the point of complete erasure from reality. Albert Einstein was the first to mathematically derive this in the formula E = mc2.

Matter can be created from energy or converted into energy through the use of processes, such as nuclear fission or nuclear fusion.

For example:

  1. human throws the stone using energy stored in muscles = chemical energy
  2. stone moves upwards = kinetic energy
  3. stone at the highest point = potential energy
  4. stone falls to ground = kinetic energy
  5. stone hits ground = thermal energy/sonic energy

Types of energyEdit

Scientists have identified many types of energy, and found that they can be changed from one kind into another. For example:

Measuring energyEdit

Energy can be measured. The amount of energy a thing has can be given a number.

As in other kinds of measurements, there are measurement units. The units of measurement for measuring energy are used to make the numbers meaningful.

The SI unit for both energy and work is the joule (J). It is named after James Prescott Joule. 1 joule is equal to 1 newton-metre. In terms of SI base units, 1 J is equal to 1 kg m2 s−2. It is most often used in science, though particle physics often uses the electronvolt.

The measurement for electricity most often uses the kilowatt-hour (kW·h). One kW·h is equivalent to 3,600,000 J (3600 kJ or 3.6 MJ).

Related pagesEdit


  1. Woolley, Steve (2011). Edexcel IGCSE Physics Revision Guide. Pearson Education. p. 49. ISBN 9780435046736.