Moments, Levers and Gears
Master Moments, Levers and Gears for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) physics topic: the moment of a force is M = Fd, and levers and gears use moments to transmit the turning effect of a force.
Free downloads
These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
A force or system of forces may cause an object to rotate. The turning effect of a force is called the moment. This is a Triple-only topic.
The equation is moment = force × distance, where the distance is the perpendicular distance from the pivot to the line of action of the force. Moment is measured in newton-metres.
If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment. This is the principle of moments. Levers and gears both transmit the rotational effect of forces — a lever allows a smaller force to have the same moment by acting at a greater distance from the pivot.
Revision notes
The equation
Moment = force × distance, M = Fd.
The distance is the perpendicular distance from the pivot to the line of action of the force. Force in newtons, distance in metres, moment in newton-metres.
The principle of moments
If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment.
This allows an unknown force or distance to be calculated. Set the two totals equal and solve.
Levers and gears
A lever allows a smaller force to have the same moment by acting at a greater distance from the pivot — a force multiplier.
Gears transmit rotational effects. A larger gear turns more slowly but with a greater moment than a smaller gear driving it.
Key points
- A moment is the turning effect of a force.
- Moment = force × perpendicular distance from the pivot.
- Moment is measured in newton-metres.
- When balanced, clockwise equals anticlockwise moment.
- A lever is a force multiplier.
- Gears transmit rotational effects.
Worked examples
Example 1
A force of 20 N acts at a perpendicular distance of 0.5 m from a pivot. Calculate the moment. [2 marks]
Model answer
Moment = force × distance = 20 × 0.5 (1 mark) = 10 Nm (1 mark).
Example 2
State the principle of moments. [2 marks]
Model answer
When an object is balanced, the total clockwise moment about a pivot (1 mark) is equal to the total anticlockwise moment about that pivot (1 mark).
Example 3
A 30 N force acts 0.2 m from a pivot on one side. Calculate the distance at which a 15 N force must act on the other side to balance it. [3 marks]
Model answer
Clockwise moment = 30 × 0.2 = 6 Nm (1 mark). For balance the anticlockwise moment must also be 6 Nm, so 15 × d = 6 (1 mark). d = 6 ÷ 15 = 0.4 m (1 mark).
Common mistakes
Using a distance that is not perpendicular.
The distance must be measured perpendicular to the line of action of the force.
Giving the unit as newtons.
Moment is measured in newton-metres.
Forgetting to equate the two moments.
For a balanced object, clockwise total equals anticlockwise total.
Measuring distance from the force rather than the pivot.
The distance is always measured from the pivot.
Exam tips
- Use the perpendicular distance from the pivot.
- State newton-metres as the unit.
- Set clockwise equal to anticlockwise for balance problems.
- Remember this is a Triple-only topic.
Key terms
- Moment
- The turning effect of a force, in newton-metres.
- Pivot
- The fixed point about which rotation occurs.
- Principle of moments
- Clockwise moment equals anticlockwise moment when balanced.
- Lever
- A device allowing a smaller force to produce the same moment.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.