Moments (CIE A Level Physics)

• A moment is the turning effect of a force
• Moments occur when forces cause objects to rotate about a pivot

• The moment of a force is given by the equation:

• Where:
  • moment = turning effect in newton metres (N m)
  • F = force in newtons (N)
  • d = perpendicular distance from the pivot in metres (m)

• The force may not always be applied perpendicularly to the pivot
• However, the distance used in the equation must be the perpendicular distance from the pivot
• In these cases, the component of the distance that is perpendicular to the pivot must be used

Force applied at an angle to the pivot

When the force is applied at an angle to the pivot, the component of the distance that is perpendicular must be used

• An example of moments in everyday life is opening a door
  • The door handle is placed on the opposite side of the door to the hinge (the hinge is the pivot)
  • This maximises the distance for a given force
  • Which provides a greater moment (turning effect)
    • This makes it easier (requires less force) to push or pull the door open