Moments & Stability Lab
Move forces on a beam, compare clockwise and anticlockwise moments, and connect centre-of-gravity ideas to stability.
Learning goals
- Describe a moment as a force's turning effect in everyday examples
- Apply moment = force × perpendicular distance from the pivot
- State the principle of moments for a body in equilibrium
- apply the principle of moments to new situations or to solve related problems
- show an understanding that the weight of a body may be taken as acting at a single point known as its centre of gravity
Learning objectives
- Describe a moment as a force's turning effect in everyday examples
- Apply moment = force × perpendicular distance from the pivot
- State the principle of moments for a body in equilibrium
- apply the principle of moments to new situations or to solve related problems
- show an understanding that the weight of a body may be taken as acting at a single point known as its centre of gravity
- Explain qualitatively how centre-of-gravity position affects stability
Metre rule pivoted at 50 cm with loads of 3.0 N at 20 cm, 2.0 N at 85 cm. Clockwise moments 0.70 newton metres, anticlockwise moments 0.90 newton metres. The rule is held level.
- Sum of clockwise moments
- 0.70 N m
- Sum of anticlockwise moments
- 0.90 N m
- Resultant moment
- 0.20 N m anticlockwise
- Tilt
- 0 °
- Line of action of the weight
- inside the base
Try this
0 of 4 doneBalance the rule with unequal loads, then let go. (not done yet)
The rule stays level when the sum of clockwise moments equals the sum of anticlockwise moments: a smaller load needs a longer distance.
Balance the rule with the pivot away from the 50 cm mark. (not done yet)
The rule's own weight acts at its centre of gravity, so it has a moment about any pivot that is not at the centre.
Tilt the block so that it only just topples when you let go. (not done yet)
The block topples once the line of action of its weight passes outside its base, beyond the edge it pivots on.
Change the block so that it falls back upright after a 30° tilt. (not done yet)
A lower centre of gravity and a wider base make the block more stable: it must tilt further before its weight acts outside the base.