Moment
Science: KS3, topic 3.2.15
Moments
The turning effect of force around a pivot or fulcrum is called a moment. The moment depends on two factors.
Moments
- The turning effect of a force around a pivot or fulcrum is called the ‘moment’.
- The size of the moment depends on two factors:
- The amount of force applied. The greater the force the greater the moment.
- The distance from the pivot/fulcrum to where the force has been applied.
- So a mechanic will find it easier to undo a wheel nut if he or she uses more force and/or uses a longer spanner.
Moments on a seesaw
- On a seesaw, the moment may act in a clockwise or anticlockwise direction.
- If nobody was on the seesaw, there would be no force acting on it. So it would be level and the moments would be equal and balanced.
Moment on a seesaw 2
- For a balanced seesaw:
- Total clockwise moment = total anticlockwise moment.
- If somebody got on the righthand side of the seesaw, the seesaw would move in the clockwise direction as the moments would be unbalanced.
- If somebody got on the lefthand side of the seesaw, the seesaw would move in the opposite direction.
Calculating moments
- The unit of a moment is Newton metre (Nm).
- Moment (Nm) = force (N) x perpendicular distance from the force to the pivot (m).
- Perpendicular means a straight line from the pivot to the force.
Moments - customs question
- If a customs official opens a wooden crate with a 1.5m crowbar by applying a force of 30N, what is the turning effect?
- Moment = 1.5 x 30 = 45Nm.
Test yourself on Moment
What are the units for moment?
Select the true statement about moments and seesaws
A seesaw is balanced with two children sitting at equal distances from the pivot. One child moves closer to the pivot while the other child stays in the same place. What happens to the seesaw?