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 a moment is when you push a door open. As 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). In this case, the moment is created by you pushing the door, and the result of this moment is the door’s rotation around its hinges.

The action of opening a door serves as a practical example of moments, especially when considering how a door is designed. 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 the point where the force is applied, the larger the moment will be—meaning a greater turning effect.

It’s also important to note that the greater the distance between the pivot and the point where the force is applied, the less force is 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 is how using a lever or a crowbar can help you move heavier objects

It’s important to remember:

Physical QuantitySymbolUnitUnit Symbol
MomentMNewton-metresN m or N·m