A box is gradually tilted on its bottom-right edge. The diagrams show three stages. The dot marks the centre of gravity. At which stage does the box first t...
Question 1 Report
A box is gradually tilted on its bottom-right edge. The diagrams show three stages. The dot marks the centre of gravity.
At which stage does the box first topple over?
Answer Details
An object topples when the vertical line drawn downward from its centre of gravity falls outside its base of support. At Stage 1 the box sits flat on the ground, so the centre of gravity is directly above the middle of the base and the box is stable. At Stage 2 the box is tilted on its bottom-right edge, but the vertical line through the centre of gravity still falls within (or on the edge of) the base, so the box would return to its original position if released.
At Stage 3 the tilt is large enough that the vertical line through the centre of gravity passes beyond the pivot edge. Once this happens, the weight of the box creates a turning moment that rotates it further away from the upright position rather than back towards it, and the box topples over.
The key principle is that stability depends on the horizontal position of the centre of gravity relative to the base. A wider base or a lower centre of gravity makes an object harder to topple. In examination questions involving tilting, always check whether the centre of gravity still lies above the support region.
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