Define the moment of a force as moment = force × perpendicular distance from the pivot; recall and use this equation

What is a Moment?

The moment of a force (also called torque) tells us how strong a force is at making something rotate about a pivot point.

It is calculated with the simple formula:

\$M = F \times d_{\perp}\$

Where:

• \$F\$ = magnitude of the force (in newtons, N)
• \$d_{\perp}\$ = perpendicular distance from the pivot to the line of action of the force (in metres, m)

The product gives the moment in newton‑metres (N·m).

Why “perpendicular” distance?

Imagine a seesaw. If you push at the very end, the lever arm is long and the seesaw tilts easily.

If you push closer to the centre, the lever arm is short and you need a bigger force to tilt it.

The key is the distance that is perpendicular to the direction of the force – that’s the part that actually pushes the lever away from the pivot.

Analogy: Door Knob

Think of turning a door knob. The force you apply is the hand’s push, and the distance from the knob to the hinge is the lever arm.

The farther your hand is from the hinge, the easier it is to open the door – that’s a larger moment.

Exam Tips 🎓

• Always identify the pivot point first.
• Use the perpendicular distance – if you’re unsure, draw a line from the pivot to the line of action of the force.
• Check the sign of the moment (clockwise vs counter‑clockwise) – remember the right‑hand rule or the “hand on the lever” trick.
• Units: moment is always in N·m. 1 N × 1 m = 1 N·m.
• When a problem gives you a moment and you need the force, rearrange the formula: \$F = \dfrac{M}{d_{\perp}}\$.
• Look for “turning effect” or “torque” in the question wording.