Moments and levers · Grade 11
A force can make something turn about a pivot. The turning effect is called a moment, and it depends on both the force and how far from the pivot it acts. When an object is balanced, the clockwise moments equal the anticlockwise moments: this is how seesaws, cranes, spanners and wheelbarrows work.
Key facts
- Moment = force × perpendicular distance from the pivot (N m).
- Principle of moments: in balance, total clockwise moment = total anticlockwise moment.
- A longer lever or spanner gives a bigger moment for the same force.
- The weight of a uniform beam acts at its centre.
- For a force at angle θ to a lever: moment = Fd sin θ.
- A couple (two equal, opposite, parallel forces) has torque = F × distance between them.