Moment of Force

The turning effect produced when a force is exerted on an object:

Moment of force

Examples of turning effect of force:

Using scissors, picking up wheelbarrow, using crane to move things

What can forces cause?

Rotation of an object about a fixed pivot

What can rotation of an object around a fixed pivot be?

Clockwise or anti-clockwise

What will a force applied on one side of a pivot cause?

The object to rotate

Diagram of turning effect of force about a pivot:

In this case, what will the force applied cause?

The object to rotate clockwise about the pivot

Moment of force = ?

Force x perpendicular distance from pivot

Which forces will cause a moment of force on a horizon beam?

Forces directed upwards or downwards

Diagram of turning effect of force exerted on spanner:

How does increasing the distance at which a force is applied from a pivot affect the force required?

Decreases it

Is it easy to push open a door right next to the hinge?

No

Why is it difficult to push open a door right next to the hinge?

It requires a lot of force

Is it easy to push the door open at the side furthest from the hinge?

Yes

Why is it easy to push the door open at the side furthest from the hinge?

Less force is required

What does the principle of moments state?

If an object is balanced, the total clockwise moment about a pivot equals the total anti-clockwise moment about that pivot

What does the principle of moments mean?

For a balanced object, the moments on both sides of the pivot are equal

What does the principle of moments say is the relationship between the clockwise and anti-clockwise moments?

They are equal

Diagram of principle of moments:

What kind of force is applied on a beam about a pivot if the beam moves clockwise?

Clockwise force

Write an equation about the moments acting on the beam:

F2xd2 = F1xd1 + F3xd3

What moment does force F1 cause about the pivot?

Anti-clockwise moment of F1xd1

What moment does force F2 cause about the pivot?

Clockwise moment of F2xd2

What moment does force F3 cause about the pivot?

Anti-clockwise moment of F3xd3

Why is F2xd2 = F1xd1 + F3xd3?

According to principle of moments, a beam is balanced when sum of the clockwise moments = sum of the anticlockwise moments