A moment is the turning effect of a force. For an object to turn, there needs to be a pivot. When calculating a moment, it is important to know:

  • The distance between the pivot and where the force was applied
  • The size of the force exerted

To calculate a moment the equation is:

Moment = Force × Distance

An example of this is when you push a door open. When you push the handle, the door rotates around its hinges. The force you exerted caused the door to rotate around the hinges (which is the pivot). You pushing the door is the moment and the result of this moment was the door’s rotation around its hinges.

The action of opening a door is a useful application of moments when looking at the build of a door. The handle is on the opposite side of the door to the hinges. This is because the moment of a force is related to the size of force and the distance between the pivot and where the force was applied. The greater the distance from the pivot to where the force is applied, the larger the moment (turning effect).

  • It is also important to know, the greater the distance between the pivot and where the force was applied, the less force required to complete an action. For example (as you can see in the diagram below), if you try to push a door open, close to the hinges, then you will need significantly greater force.
  • Another application of moments are how using a lever or a crowbar can help you move heavier objects

It’s is important to remember:

Physical QuantitySymbolUnitUnit Symbol
MomentMNewtons-metresN m or N·m