1. Levers
A lever is a rigid body free to rotate about a fixed point called a fulcrum.

2. The moment of a force is the turning effect of a force.
Moments
The moment of a force is the turning effect of a force.
Moment = Force X Perpendicular distance to the fulcrum
When a lever is balanced the clockwise moments equal the anticlockwise moments

3. Calculations on levers
40 cm
20N X
Find the value of X that will balance the metre stick.

4. More Practise X
30 cm
20N
15cm
40N
100N
20cm
Find X in the above.

5. Equilibrium When a body is at rest it is said to be in equilibrium.
The conditions for equilibrium are
The vector sum of all forces is zero
The sum of moments about any point is zero

6. Experiment to verify the Laws of Equilibrium50
Spring balance
Weight
Retort stand

7. Method Find the weight of the metre stick using a spring balance.
Set up the apparatus as shown and adjust the position of the weights until the metre stick is horizontal and in equilibrium.
Note the weights and the readings on the spring balances.
Note the distances of all weights and spring balances from the 0cm point.
Calculate the clockwise and anticlockwise moments and the upward and downward forces.

8. Results
Clockwise
Anticlockwise
Weight N
Distance m
Moment Nm 2
0.1
0.2 16
0.15
2.4 1 3
0.8
0.45
0.9
0.5
0.6
1.2
1.8
Total
4.8Nm
4.8 Nm
Upward forces= 11N
Downward forces= = 11N