Mechanics: Moments

Key Concepts

A moment is a measure of the turning effect of a force about a point (called the pivot or fulcrum),
The size of a moment is given by the formula: Moment = Force x Perpendicular distance from pivot. It is measured in Newton meters (Nm).
When an object is in equilibrium, the total clockwise moment about any point equals the total anticlockwise moment.
The Principle of Moments states that if an object is balanced (in equilibrium), the sum of clockwise moments about any point is equal to the sum of anticlockwise moments.
Torque is another term for moment, and is often used in the context of engines and power transmission.

Calculating moment: using the formula Moment = Force x Distance, where force is measured in Newtons (N), distance is in metres (m), and the resulting moment is in Newton-metres (Nm).
To find an object’s equilibrium, add up the moments in each direction about any point - if the object is in equilibrium, these should be equal.

Analysing moments helps to understand why a tightrope walker carries a long pole (increases the distance from pivot), and how a crowbar works (increases applied force).
Understanding equilibrium of moments is critical in structure design – for instance, in bridges and skyscrapers, to ensure they remain standing.

Moments and the Principle of Moments are fundamental principles in explaining the mechanics of how levers work.
Levers can be used to amplify force by applying the force over a large distance, resulting in a larger moment.
Being able to calculate moments and understand their implications is key to understanding many physical systems, from simple levers to complex mechanical structures.