What are moments

5a) describe the moment of a force in terms of its turning effect and relate this to everyday examples.

The moment of a force, is the measure of the turning effect of a force about a fixed point. This fixed point is usually referred to as axis or pivot. The pivot is a fixed point, around which the turning effect is produced

The moment of a force = force * perpendicular distance from the pivot . Sounds difficult, right?

Let us take a daily life example where moment of a force is used.

The above is a diagram of a door viewed from above. Whenever we open the door, we apply a force
at somewhere between point A and point C. The hinge is our pivot, because whatever force we apply would cause the door to move in a circle around that fixed point, the hinge.

Now you might have noticed in your daily life that it takes less force to open a door when the force is applied nearer to point A than to point C.This is so because the perpendicular distance from the pivot/hinge is greater when the force is applied at A then compared to C. As we know that perpendicular distance from the pivot is directly proportional to the moment of a force, this means that the further away the force is applied from the pivot, the greater the turning effect is produced.

We also know that force is directly proportional to moment of a force. Therefore applying more force would produce a greater turning effect.


Let us take another daily life example of moment of forces.

In our daily life, we regularly use spanners to tighten screws. You might have noticed that if you try to tighten the screw by hand, it is almost impossible. On the other hand, when you use a spanner, it becomes much more easier to tighten the screw. This is so because the turning effect produced on the screw using a spanner is greater than that produced by using your hand.

When a spanner is used, we are actually using the turning moment of a force to our advantage. More turning effect is now produced because the perpendicular distance from the pivot/screw is now greater than before, producing a greater moment.

There are countless other examples in our daily life where moment of a force is used. Observe and figure them out!