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 $$W$$ = force $$F$$ × distance moved in the direction of the force $$x$$.
 * $$W = F x$$

or, where $$\Theta$$ is the angle between the direction of the force and the distance,
 * $$W = F x cos\Theta$$

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

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 (EK) is moving energy and potential energy (EP)is the energy that could be transferred to moving energy. The formula for these are:

Kinetic Energy: $$E_K = \frac{1}{2}mv^2$$

Potential Energy: $$E_P=mg\Delta h$$

The relationship between work done and energy is:

Work done = Energy transferred