Power calculations (P = W/t)
Lesson details
Learning outcome
I can describe power and calculate the rate at which energy is transferred by a force.
Key learning points
- Power is equal to the rate at which work is done.
- Power is equal to the rate at which energy is transferred.
- Power = work done ÷ time.
- Power is measured in watts (W).
Keywords
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).
Teacher tip
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.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.Which of these units can be used to measure energy?
Q2.Which of these is the unit of work done?
Q3.Which of these is the unit of force?
Q4.What is the equation for work done?
Q5.work done = × distance
Q6.Put these in order of decreasing work done, starting with the greatest amount of work done.
Assessment exit quiz
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?
Q2.Match the quantities to their units.
newtons (N)
watts (W)
metres per second (m/s)
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?
Q4.Which of these is the correct equation for power?
Q5.What would Aisha’s power be if she walked up the hill 4× more slowly, compared to when she ran up it?
Q6.Put these in order of decreasing power, starting with the greatest amount of power.
To help you plan your 10 physics lesson on: Power calculations (P = W/t), download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 10 physics lesson on: Power calculations (P = W/t), download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 4 physics lessons from the Energy of moving objects unit, dive into the full secondary physics curriculum, or learn more about lesson planning.