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**MOMENTS AND LEVERS**

**A lever is a rigid body that can rotate about a fixed axis at a point called the fulcrum**

**The moment of a force is that force multiplied by the perpendicular distance to the fulcrum**

d = perpendicular distance from line of force to fulcrum (m),

F = force (N)

M = moment (Nm)

Moments are useful as we can use them to amplify force, a weight of 500N can be lifted by a force of only 100N, provided there is a 5m lever arm between the force and the fulcrum

Moments are vectors, measured in Newton metres (Nm),

A positive moment denotes one that would tend to rotate the body it acts on clockwise, a negative one would tend to rotate it anticlockwise.

**The centre of gravity of a body is the point through which all of its weight appears to act**

**EQUILIBRIUM**

**A body is in equilibrium if:**

- The vector sum of the forces acting on the body in any direction is zero
- The sum of the moment of the forces about any point on the body is zero

Example: The uniform metre stick below experiences a number of forces, as well as its weight of 7N, is it in equilibrium?

Upward forces = \(12+20 = 32N \)

Downward forces = \(10+7+15 = 32N \)

Take the left end as the fulcrum

Clockwise moments = \( (10 times 0.1) + (7times 0.5) + (15times0.86) = 17.4Nm \)

Anticlockwise moments = \( (12 times 0.2) + (20 times 0.75) = 17.4Nm \)

Since the upward forces equal the downward forces and the the clockwise moments equal the anticlockwise moments, the body is in equilibrium

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