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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 part of the market where energy itself is harnessed and sold to consumers.
- In ordinary language, the word is used to describe someone acting or speaking in a lively and vigorous way.
In science energy is something that can do work.
There are two basic forms of energy:
Conservation of Energy
Here is an example:
- the energy of a thing is measured to start with
- the energy changes from potential energy to kinetic energy and back again
- at the end the energy of the thing is measured again
The measurements of energy at the start and end will always be the same.
Conservation of matter and energy
Scientists now know that matter can be made into energy, and energy into matter, through processes like nuclear fission and nuclear fusion. The law of conservation of energy has therefore been extended to become the Law of conservation of matter and energy. Albert Einstein was the first to mathematically derive this in the formula E = mc2.
A stone is thrown upwards and falls to the ground.
- human throws the stone: energy store in muscles= chemical energy
- stone moves upwards= kinetic energy
- stone at the highest point= potential energy
- stone falls to ground= kinetic energy
- stone hits ground= thermal energy/sonic energy
Types of energy
Scientists have identified many types of energy, and found that they can be changed from one kind into another. For example:
- Light energy
- Sound energy
- Renewable energy
- Solar energy
- Nuclear energy
- Elastic energy
- Gravitational potential energy
- Kinetic energy
- Dark energy
- Hamiltonian mechanics
- Internal energy
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
- Woolley, Steve. Edexcel IGCSE Physics Revision Guide. Pearson Education. p. 49. .