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

Doing Work:

A force can increase the kinetic energy or gravitational potential energy of an object. The force moves through a distance, and we say that it does work. The amount of work done tells us the amount of energy transferred by the force.

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,

Then

work done = force x distance moved in the direction of the force.

W = F x D

work done by tension = T x D

work done against friction = -F x D

work done by gravity = -mg x h

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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: $E_K=\frac{1}{2}m{v}^2$

Potential Energy: $E_P=mg\mathrm{\Delta }h$

The relationship between work done and energy is:

Work done = Energy transferred