Work is done whenever a force makes an object move. The amount of work is force multiplied by distance moved in the direction of the force.

The rate at which something changes is usually equal to the amount of change each second.

The unit for measuring power is the watt (W).

A thousand watts is called a kilowatt (kW).

Power (P = E/t)

Combined science

In the Forces make things change unit, they will build on this knowledge to learn how to combine forces in two dimensions, how to calculate acceleration from a resultant force and how to calculate forces in collisions and explosions.

In the Measuring and calculating motion unit, pupils learnt how to measure and calculate velocity and acceleration, and how to interpret displacement-time and velocity-time graphs. 

Energy of moving objects

Aisha does 6000 J of work when she runs up a hill. 
How much work does she do when she runs up the same hill in less time? 

Aisha’s power when she runs up a hill is 400 W. 
What is her power when she runs up the same hill in less time? 

Which of these is the correct equation for power?

What would Aisha’s power be if she walked up the hill 4× more slowly, compared to when she ran up it?

80 J of work is done pushing a crate 2 m in 3 seconds.

100 J of work is done lifting a load 2 m in 5 seconds.

90 J of work is done pushing a trolley 6 m in 6 seconds.

100 J of work is done pulling a boat 5 m in 10 seconds.

Put these in order of decreasing power, starting with the greatest amount of power.

Which of these units can be used to measure energy?

A boat is pulled 5 m with a force of 21 N.

A trolley is pushed 6 m with a force of 15 N.

A crate is pushed 2 m with a force of 40 N.

Put these in order of decreasing work done, starting with the greatest amount of work done.

This lesson will soon be taken down.

Power (P = E/t)

Lesson outcome