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J - Factary




The unit of energy in the SI system of units.

One joule of work is done when a force of one newton moves a distance of one metre in the direction of the force.

It’s perhaps clearer if we use the example of a force being used to move something, rather than just saying the force moves. In order to lift something up (in other words move it against the force of gravity), we need to apply a force to that object. The force of gravity on a mass of 0.1 kg is 1 newton. To lift such a mass, we need to apply a force of 1 newton to the mass in the vertical direction. Therefore, if we lift 0.1 kg, or 100 gms, vertically up by a distance of 1 metre, we have used 1 joule of energy.

1 kJ (kilojoule) = 1000 J
1 MJ (megajoule) = 1,000,000 J


Joule, James Prescott (1818-1889)


James Prescott Joule was born in Salford in England. He was one of the outstanding scientists of his time. Joule is best known for his work in electricity and thermodynamics (the movement of heat).


Joule first suggested the law which is named after him today. It states that the amount of heat given off by an electrical conductor is proportional to the square of the current passing through it. He also made very accurate scientific instruments, one of which he used to measure the energy which was transferred in a waterfall, showing once again that energy is just transferred, not created or destroyed.


The unit of energy called the joule is named after him.


Together with William Thomson (later Lord Kelvin), Joule found that the temperature of a gas falls when it expands. This is the principle behind most refrigerators and air conditioning systems. Cool stuff!


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