What is the moment of a force? State the principle of moments and give its applications.

1. 1 · Define moment in one line. The moment of a force (torque) is its turning effect about an axis: τ = F × d. Unit N m.
2. 2 · Explain with a see-saw. A force F₁ at distance d₁ turns the plank one way; F₂ at d₂ turns it the other way.
3. 3 · State the principle. In equilibrium, the sum of clockwise moments = the sum of anticlockwise moments: F₁ × d₁ = F₂ × d₂.
4. 4 · Give applications.
   • Gears change the speed of rotation by changing torque.
   • A see-saw balances by changing the distances.
   • A steering wheel gives a large torque with a small force.
5. 5 · Real-life link. Beam balance in a shop, door handles, long spanners.
6. 6 · Close in one line. The turning effect depends on both the force and its distance from the pivot.

Scoring tip: Write the formula F₁ × d₁ = F₂ × d₂ and add a short numerical. It earns the full 4 marks quickly.