Work – GCSE Physics (Combined) CCEA Revision

Work Done

Work is done when a force moves an object through a distance.
It is measured in joules (J), the SI unit for work or energy.
When a force causes a displacement in the direction of the force, it is said that work is done on the object.
Work done = Force(N) x Distance(m).
The amount of work done depends on the size of the force and the distance moved.
If there is no movement, even if force is applied, there is no work done.
Work done against the gravitational force in lifting objects is given by the equation: Work done = Weight(N) x Height(m).

In lifting: The work done on an object being lifted is equal to the weight of the object being lifted times the height to which it is lifted.
In stretching: Work done on an elastic object like a spring is equal to the force applied times the distance the spring is stretched.
In pushing: When an object is pushed along a horizontal surface, work done is equal to the force applied times the distance moved.

Work done on an object can be seen as energy transfer.
When work is done, the energy is transferred from one form to another; often this energy is transferred as either kinetic energy or potential energy.
For instance, raising an object transfers energy to it, increasing its gravitational potential energy.
Increasing the speed of an object transfers energy to it, increasing its kinetic energy.

Work done can be analysed using force-displacement graphs.
The area under a force-displacement graph represents the work done.
The gradient of a force-displacement graph is the force applied.
If the force is constant, the graph of force versus displacement is a straight line. The work done is equal to the area under the line.

The greater the work done on an object, the greater the amount of energy transferred.
Work done can result in an increase in temperature. For example, when you rub your hands together rapidly, work done by the friction force heats up your hands.