5.3 Mechanics

Question 1

Moment

Answer 1

The turning effect of a force about a pivot.
M = Fd

M = moment in newton metres (Nm)
F = force in newtons (N)
d = perpendicular distance of the force to the pivot in metres (m)

Question 2

Principle of moment

Answer 2

If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot.
Moment = force × distance from a pivot
The forces should be perpendicular to the distance from the pivot.

Question 3

Levers

Answer 3

Levers increase the size of a force acting on an object to make the object turn more easily.
The force applied to a lever must act further from the pivot than the force has to overcome.
To make a lever work better:
Increase the size of the force applied.
Increase the distance of the force from the pivot.

Question 4

Gears

Answer 4

Gears, similar to levers, multiply the effect of a turning force using moments
They consist of wheels with toothed edges that rotate on an axle or shaft, which acts as the pivot.
The teeth of one gear fit into the teeth of another gear.
This lets one gear turn the other, meaning one axle or shaft can be used to turn another shaft.
As one gear turns, the other must also turn.
One of the gears will then move clockwise, and the other anticlockwise (in opposite directions).
Although the force will be the same on both gears, the moment will not be. This depends on the size of the gear, which changes the distance of the teeth to the pivot (axle).
If a larger gear is driven by a smaller gear, the large gear will rotate slower than the smaller gear but will have a greater moment.
If a smaller gear is driven by a larger gear, the smaller gear will rotate quicker than the larger gear but will have a smaller moment.
This is because the turning force on the larger gear wheel acts further from its pivot than the turning force of the smaller gear wheel acting on its own pivot.