Moment of Force
Sometimes, a force can cause an object to rotate. For example, when a force is applied to the end of a spanner, a turning effect will be produced, which helps to screw or unscrew a nut.
The turning effect produced by force is called a moment. The magnitude of moment can be calculated by multiplying the magnitude of the force by the perpendicular distance from the pivot.
Moment = F x d
Moment (N·m)
F = force (N)
d = perpendicular distance between force and pivot (m)
Describe how the lever-arm is used to move the bolt, and suggest why the spring is needed.
- If you push the lever-arm to the left, the bolt will move to the left. The spring is needed to return the lever-arm to the right.
The force applied at point B is 22 N. The pivot is 110 cm from point B and 38 cm from point A. Calculate the force exerted on the lever-arm at point A by the spring.
- The moment caused by the force applied at B with respect to the pivot is equal to the moment caused by the force at A with respect to the pivot.
(22 N) x (110 cm) = FA x (38 cm)
FA = (22 N) x (110 cm) / (38 cm) = 64 N
Explain how the force applied at point B would need to change if the distance from the pivot to point A is increased.
- Since the distance to from the pivot to A increased, the moment will also have increased.
- The distance from the pivot to B remains constant.
- For the moment to have increased while the distance remains constant, the force applied at point B should have increased.