1. Moments – Learning Outcomes
Recall two everyday applications of levers.
Solve problems about moments.
HL: Investigate the law of the lever.

2. Recall Applications of Levers
When objects cannot move, but can swing/turn around a point, we call it a lever.
A lever is a rigid object which is free to turn about a fixed point called a fulcrum.
e.g. door handle, scissors, wheelbarrow

3. Solve Problems About Moments
For a lever to turn, a force must be applied to it.
The “turning effect” of a force can change in one of two ways:
change the force being applied, or
change the distance from the force to the fulcrum.

4. Solve Problems About Moments
The moment of a force is the force times the perpendicular distance from the force to the fulcrum.
𝑀=𝐹×𝑑
e.g. A man opens a door by applying a force of 5 N to the door. The distance from the point of application of the force to the fulcrum is 120 cm.
Calculate the moment of the applied force.

5. Solve Problems About Moments
e.g. The diagram shows a crane in equilibrium.
What is the moment of the 9000 N concrete slab about the axis of the crane?
Calculate the value of the load marked X.

6. Solve Problems About Moments
e.g. Which has a greater moment for the spanner shown:
9 N applied 8 cm from the fulcrum, or
30 N applied 3 cm from the fulcrum

7. HL: Investigate the Law of the Lever
The Law of the Lever states: when a lever is balanced, the clockwise moment acting on it is equal to the anti- clockwise moment.

8. HL: Investigate the Law of the Lever
e.g. is the lever below balanced?

9. HL: Investigate the Law of the Lever
e.g. The lever below is balanced. What is the value of x?

10. HL: Investigate the Law of the Lever
e.g. The lever below is balanced. What is the value of 𝑦?

11. HL: Investigate the Law of the Lever
Hang a metre stick at the 50 cm mark.
Attach two known weights and adjust their positions until the metre stick balances.
Measure the distance of the weights from the 50 cm mark.
Verify that the clockwise moment equals the anti- clockwise moment by formula.