Starter quiz
- Which of the following statements about moments is correct?
- A moment is a turning force.
- A moment is the turning effect of a force. ✓
- A moment is the angle of a rotation.
- A moment is a rotation.
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- A force of 40 N acts at a distance of 10 m normal to a pivot. The moment produced by the force is ______ Nm.
- '400' ✓
- A moment of 50 Nm is produced by a force of 20 N. The perpendicular distance between the direction of the force and the pivot is ______ m.
- '2.5' ✓
- A moment of 300 Nm is produced by a force acting at a distance of 50 cm from a pivot. The magnitude of the force is ______ N.
- '600' ✓
- Which of the following statements for an object with no resultant force or moments acting on it are correct?
- There are no forces acting on the object.
- The object is not accelerating. ✓
- The object is moving.
- The object is stationary.
- The object is in equilibrium. ✓
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The diagram shows a metre rule of weight 5 N balanced on a support. Two objects, of weight 2 N each, are placed on it as shown. What is the size of the upwards force labelled ?- 1 N
- 2 N
- 4 N
- 5 N
- 9 N ✓
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Exit quiz
- Which of the following statements describes the principle of moments?
- A moment is the turning effect of a force.
- An object balances when there are no moments on it.
- An object balances when there is no resultant moment on it. ✓
- Moment = force × distance normal to the force direction.
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The diagram shows a balance beam in equilibrium. There are four forces acting on it: , , and . Which of the following statements are correct?-
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- ✓
- ✓
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A pupil has two masses, labelled X and Y. One of the masses is twice as heavy as the other. The pupil places the masses on a balance beam, as shown. Which of the following statements are correct?- Mass Y must be heavier than mass X.
- To balance the beam, mass X should be moved towards the left. ✓
- To balance the beam, mass Y should be moved towards the left. ✓
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The diagram shows a beam with three forces acting on it. Which of the following statements are correct?- The total clockwise moment is 15 Nm. ✓
- The total clockwise moment is 21 Nm.
- The total clockwise moment is 24 Nm.
- The beam is balanced.
- The beam is unbalanced. ✓
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The beam shown in the diagram is balanced. What is the distance ?- 0.30 m ✓
- 0.90 m
- 1.2 m
- 8.3 m
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The beam shown in the diagram is balanced. What is the size of the force ?- 15 N
- 24 N
- 48 N ✓
- 60 N
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Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- Moment = force × distance (M = Fd)
- If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment.
- An object is in equilibrium if it is balanced and there are no resultant forces acting.
Common misconception
The distance to a pivot is always the distance along the lever, no matter which direction the force is acting in.
Opening a door by pushing on the handle in different directions shows it is harder to open when the shoulder of the person pushing is closer to the pivot (smaller perpendicular distance between the force and the pivot).
Keywords
Equilibrium - The state of an object when there is no resultant force or moment acting on it.
Moment - The turning effect of a force, measured in newton metres (Nm).
Principle of moments - An object will balance when the clockwise moments are equal to the anticlockwise moments.
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