Work - 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.
Power - Power is the rate at which work is done.
Rate - The rate at which something changes is usually equal to the amount of change each second.
Watt (W) - The unit for measuring power is the watt (W).
Kilowatt (kW) - A thousand watts is called a kilowatt (kW).

Common misconception

Pupils often mix up the terms power and force, which are often used interchangeably in everyday speech.

Provide opportunities for pupils to describe events in which the terms need to be used appropriately, for example in lifting two different sized weights (different forces) whilst increasing their energy at the same rate (same power).

This lesson provides a good opportunity for pupils to practise measuring power by moving up the stairs, step-ups onto a low platform or lifting objects of different weights (avoids pupils using their own weight) in order to develop a better understanding of the numbers in power calculations.

Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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Starter quiz

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6 Questions

Q1.

Which of these units can be used to measure energy?

kilogram

Correct answer: kilojoule

kilometre

kilowatt

Q2.

Which of these is the unit of work done?

gram

Correct answer: joule

newton

watt

Q3.

Which of these is the unit of force?

joule

kilogram

metre

Correct answer: newton

Q4.

What is the equation for work done?

Correct answer: work done = force × distance

work done = force × time

work done = force ÷ distance

work done = force ÷ time

Q5.

work done = × distance

Correct Answer: force, F

Q6.

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

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

2 - A 51 N load is lifted 2 m.

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

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

Exit quiz

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6 Questions

Q1.

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?

less than 6000 J

Correct answer: 6000 J

more than 6000 J

Q2.

Match the quantities to their units.

Correct Answer:force,newtons (N)

newtons (N)

Correct Answer:power,watts (W)

watts (W)

Correct Answer:speed,metres per second (m/s)

metres per second (m/s)

Correct Answer:work done,joules (J)

joules (J)

Q3.

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?

less than 400 W

400 W

Correct answer: more than 400 W

Q4.

Which of these is the correct equation for power?

power = work done × distance

power = work done ÷ distance

power = work done × time

Correct answer: power = work done ÷ time

Q5.

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

4× greater

2× greater

the same

2× smaller

Correct answer: 4× smaller

Q6.

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

1 - 80 J of work is done pushing a crate 2 m in 3 seconds.

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

3 - 90 J of work is done pushing a trolley 6 m in 6 seconds.

4 - 100 J of work is done pulling a boat 5 m in 10 seconds.