Energy

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Energy is a word with more than one meaning.

  • 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. It can be transferred between objects, and converted in form. It cannot be created or destroyed.
  • It may also be used in economics to describe 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.

Scientific energy[change | change source]

In science, energy is the ability to do work.

Basic forms of energy include:

Conservation of Energy[change | change source]

Energy is a property that is not created or destroyed, although energy can change in 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 a closed 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.

Example[change | change source]

A stone is thrown upwards and falls to the ground.

  1. human throws the stone: energy store 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 energy[change | change source]

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

Measuring energy[change | change source]

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.

Some scientific units of measurement[change | change source]

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.

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

Related pages[change | change source]

References[change | change source]

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