Moment of Force Calculator
Calculate the turning moment of a force about a pivot.
What is the Moment of Force Calculator?
A moment of force calculator works out the turning effect (moment, sometimes called torque) that a force produces about a pivot point, based on the size of the force and how far from the pivot it's applied. It works using the standard formula moment = force × perpendicular distance from the pivot, measured in newton-metres (Nm) — this is the same principle behind why a longer spanner makes it easier to turn a stiff bolt, since the same force applied further from the pivot produces a larger moment. To calculate it manually, multiply the force in newtons by the perpendicular distance in metres between the line of action of the force and the pivot point — if the force isn't applied exactly perpendicular to the lever, only the perpendicular component of that force contributes to the moment.
How it works
A moment (also called torque) measures the turning effect of a force around a pivot point, calculated as the force multiplied by the perpendicular distance from the pivot to the line along which the force acts. This is why a longer lever arm makes it easier to turn something with the same amount of force — the moment increases with distance from the pivot, even though the force itself hasn't changed.
UK context
This principle underlies everything from using a spanner (a longer handle gives more turning force for the same hand-applied effort) to see-saws balancing, to how door handles are positioned as far as practical from the hinge for mechanical advantage.
Tips
- Only the perpendicular component of the force contributes to the moment — if a force is applied at an angle rather than perfectly perpendicular to the lever arm, only part of it produces a turning effect.
- Doubling the distance from the pivot doubles the moment for the same force — this is why longer levers and spanners make turning easier.
Frequently asked questions
What's the difference between moment and torque?
In practice, the terms are used largely interchangeably in physics and engineering — both describe the turning effect of a force around a pivot, calculated as force × perpendicular distance.
Why does a longer spanner make it easier to undo a tight bolt?
Because moment equals force × distance from the pivot — a longer handle means the same hand-applied force is multiplied by a greater distance, producing a larger turning moment on the bolt.
A quick note
Uses moment = force × perpendicular distance from the pivot. If the force isn't applied perpendicular to the lever, only its perpendicular component contributes.