Moments, Levers and Gears [H]

This lesson covers moments, levers, and gears as required by the AQA GCSE Physics specification (4.5.5). This is Higher Tier only content. A moment is the turning effect of a force. Understanding moments is essential for explaining how levers, gears, and other rotating systems work in everyday life and in engineering.

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What Is a Moment?

A moment is the turning effect of a force about a pivot (also called a fulcrum). When you push a door handle, turn a spanner, or use a see-saw, you are applying a moment.

The moment of a force is calculated using:

M = F x d

Where:

• M = moment of the force (newton metres, Nm)
• F = force applied (newtons, N)
• d = perpendicular distance from the pivot to the line of action of the force (metres, m)

Key points:

• The moment depends on both the size of the force and the distance from the pivot.
• The distance must be the perpendicular (at right angles) distance from the pivot to the line of action of the force.
• Moments can be clockwise or anticlockwise.