IGCSE Physics · Simulation · 1.5.2 Core
Balance the beam
What is the principle of moments?
The principle of moments says that when an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment. A moment is a force × its perpendicular distance from the pivot, in newton metres (N m), so a small force far from the pivot can balance a large force close to it.
The beam is held level. Which way will it tip when you let go?
- Anticlockwise moment
- ?
- 6 N × 0.30 m
- Clockwise moment
- ?
- 4 N × 0.30 m
- Result
- Held level
- Let go to find out
Tasks0 of 3 done
- Make the beam balance.
- Balance it with the two weights at different distances.
- Balance 8 N on one side with 2 N on the other.
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What to take away
- A moment is a force × its perpendicular distance from the pivot, measured in N m.
- A beam balances when the clockwise moments equal the anticlockwise moments.
- A small force far from the pivot can balance a large force close to it.
Common mistakes
- Treating the heavier side as the side that goes down, whatever the distances.
Questions
What is the principle of moments?
The principle of moments says that when an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment. A moment is a force × its perpendicular distance from the pivot, in newton metres (N m), so a small force far from the pivot can balance a large force close to it.
Does the heavier side of a beam always go down?
No. What decides it is the moment on each side, force × distance from the pivot. A 4 N load 3 m from the pivot (12 N m) outweighs a 6 N load 1 m away (6 N m), so the lighter side goes down.
What is the unit of a moment?
The newton metre, N m: a force in newtons multiplied by a distance from the pivot in metres.
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