1. Unit 9L Lesson 5 Moments
Objectives: to understand the variables on which moments depend, to be able to calculate moments, to able to understand the principle of centre of gravity, and to be able to predict of systems are balanced.
Targets: 15-24
Moments Activity

2. Turning
When objects turn or spin they have to be turning around something. This something is called the pivot point.
The pinwheel spins around its pivot point at its centre.

3. Moments
Both child A and child B have the downward force of gravity on them.
Right now child A is moving down so there is an anti-clockwise turning force on the see saw.
If B has more force than A she will go down.
This will create a clockwise turning force on the pivot.
This turning force is called the moment of the force. A B
Pivot

4. Factors Affecting Moments
The size of the force will affect the moment. The larger the force the larger the moment.
The see saw turns clockwise because there is a greater force applied to the right hand side.

5. Moment = force x distance of force from pivot
Calculating Moments
The formula to calculate moments is:
Moment = force x distance of force from pivot
M = f x d
The unit for moments is the Newton meter (Nm)
To calculate this you can also use an equation triangle

7. The Principle of Moments
If the two forces on a see saw are the same the see saw will be balanced.
This is called the principle of moments and is stated as:
total clockwise moments = total anti-clockwise moments
Try these questions for practice!

8. Work to Do Complete questions 1-5 page 131 and 1-3 page 133. Homework:
Complete H/W Sheet 10.4 and 10.5
Define the following keywords:
centre of gravity, moment, pivot, principle of moments

9. Factors Affecting Moment
The distance of the force from the pivot will affect the turning force. The greater the distance the more force.
The see saw turns anti-clockwise because there is a greater distance from the pivot on the left hand side..