Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
9.7P Recall and use the equation: moment of a force (newton metre, N m) =…
Full specification wording
Topic 9 – Forces and their effects: 9.7P Recall and use the equation: moment of a force (newton metre, N m) = force (newton, N) × distance normal to the direction of the force (metre, m)
A moment measures the turning effect of a force about a pivot.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 7 of 9
Study notes
From the checked teaching notes for this specification point.
The idea
A moment measures the turning effect of a force about a pivot. The equation is moment = force × perpendicular distance from the pivot to the line of action of the force, with moment in newton metres (N m), force in newtons (N) and distance in metres (m). The word 'normal' means the distance must be measured at right angles to the force's direction, not along the lever at an angle. For example, a 20 N force applied 0,50 m from a pivot at right angles gives 20 N × 0,50 m = 10 N m. If the force acts at an angle, resolve to find the perpendicular component or use the perpendicular distance. A larger force or a larger perpendicular distance increases the moment, which is why long spanners loosen tight nuts more easily.
What earns the marks
- Selects the equation moment = force × perpendicular distance from the pivot.
- Uses the distance measured normal (at right angles) to the direction of the force.
- Substitutes force in newtons and distance in metres to give a moment in newton metres.
- Calculates a moment correctly, for example 20 N × 0,50 m = 10 N m.
- Recognises that increasing the perpendicular distance increases the turning effect for the same force.
Common mistakes and how to put them right
Uses the slant distance along the lever instead of the perpendicular distance.
Put it right: Measure the distance normal to the force's line of action.
Adds force and distance instead of multiplying them.
Put it right: Apply moment = force × distance.
Forgets to convert centimetres to metres before multiplying.
Put it right: Divide the centimetre value by 100 first.
Gives the moment in joules or newtons.
Put it right: State the unit as newton metres (N m).
Exam tips
- Underline the words 'normal to the direction of the force' so you remember to use the perpendicular distance.
- Convert every distance to metres before substituting into the equation.
- Check the unit of your answer: a moment is measured in N m, not N or J.
Try the lesson
The start of the Topic 9 – Forces and their effects: 9.7P Recall and use the equation: moment of a force (newton metre, N m) = force (newton, N) × distance normal to the direction of the force (metre, m) lesson, made from checked teaching notes for this specification point.
Have a go first
A force of 20 N acts at a perpendicular distance of 0.5 m from a pivot. Calculate the moment of the force.
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Topic 9 – Forces and their effects: 9.7P Recall and use the equation: moment of a force (newton metre, N m) = force (newton, N) × distance normal to the direction of the force (metre, m)
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge