The turning effect of a force, M = Fd, the principle of moments for a balanced beam, and how levers and gears multiply forces.
What you will learn
- Calculate a moment with M = Fd
- Use the principle of moments to find a force or a distance
- Explain how levers and gears act as force multipliers
The turning effect of a force
A force can make an object turn about a pivot.
Its turning effect is its moment.
moment of a force = force × distance
M = F d
M in newton metres (N m), F in N, d in m: the perpendicular distance from the pivot to the line of the force. All three boards: recall.
- A 20 N push on a door, 0.75 m from the hinges
- M = 20 × 0.75
- M = 15 N m
Rearranged: force F = M ÷ d, and distance d = M ÷ F.
Change cm to m for an answer in N m. A longer spanner gives the same moment with a smaller force.
The rest of this lesson and its 10 practice questions are locked.
In this lesson
- The turning effect of a force
- Balanced beams
- Levers and gears
- Try it: Moments
10 practice questions, marked as you go; about 25 minutes in all.
Key terms
Moment, Perpendicular, Principle of moments, Lever, Gears
In this unit: Forces, work, elasticity, moments and pressure
Weight and resultant forces, work done, stretching springs and their required practical, moments, levers and gears, and pressure in fluids.