# A-level Physics/Forces, Fields and Energy/Work and energy

**Doing Work:**

Work is done whenever a force moves something over a distance. The force moves through a distance, and we say that it does work. The amount of **work done** tells us the amount of energy that has been transferred by the force. Thus:

work done (J) = energy transferred (J)

To calculate the amount of work done W, we need to know two quantities:

- The magnitude of the force F. - The distance, d, moved by the force, in the direction of the force/parallel to the force.

So Work done = force × distance moved in the direction of the force .

or, where is the angle between the direction of the force and the distance,

Force is measured in and distance travelled parallel to the force in . Thus, Work done is described in newton metres or . This is the SI unit, joule, . work done by tension &= T \times D\\ work done against friction &= -F \times D\\ work done by gravity &= -mg \times h\\ \end{alignat} </math>

**Energy:**

__James Joule is the man,__ where the term 'the joule' comes from. His principle of conservation of energy states that:

While energy may be converted from one form to another, the total amount of energy in a closed system is always constant.

There are two main different types of energy; kinetic and potential. Kinetic energy (E_{K}) is moving energy and potential energy (E_{P})is the energy that could be transferred to moving energy. The formula for these are:

Kinetic Energy:

Potential Energy:

The relationship between work done and energy is:

Work done = Energy transferred

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