workEnergy transferred by a force. Work done = force × distance moved in the direction of the force. is done when energy is transferred from one store to another. Work is also done when a force causes an object to move. When work is done against frictional forces acting on an object, the object’s temperature increases. For example, a person’s hands warm up when they rub them together repeatedly.
Learn more on work done and energy transfer in this podcast
To calculate the work doneThe amount of energy it takes to do a task. Measured in joules (J). For example, the work done in raising a mass through 10 m would be equal to the gain in potential energy of the mass. on an object when a force moves it, use the equation:
work done = force × distance
This is when:
work done is measured in joules (J)
force is measured in newtons (N)
distance moved along the line of action of the force is measured in metres (m)
Note that one joule of work is done when a force of one newton causes a movement of one metre. This means that work done can also be measured in newton-metres (Nm).
1 J = 1 Nm
It is important not to confuse newton-metres (a unit of work done) with Newton meters (calibrated spring balances used to measure weights).
Example
A doctor weighs 600 N. A lift moves her 40 m to the top floor of a hospital. Calculate the work done on the doctor by the lift.
work done = force × distance
work done = 600 N × 40 m
work done = 24,000 J (or 24 kJ)
Question
In a scrum, a rugby team pushes the other team backwards 5 m using a force of 1,000 N. Calculate the work done moving the other team.
