Understanding the Moment of a Force

The moment of a force is the measure of its turning effect on a body about a specific point.
If a force has no distance from the turning point, it creates no moment; as this distance or the force increases so does the turning effect or moment.
The moment of a force is calculated using the formula moment = force x distance, where the force is in newtons (N) and the distance is in metres (m). The unit of moment is the newton-metre (Nm).
The distance in the formula for the moment of a force is actually the perpendicular distance from the turning point or pivot to the line of action of the force.

The Principle of Moments

The Principle of Moments states that for an object to be in equilibrium, the total clockwise moments about a pivot must equal the total anticlockwise moments. Equilibrium means that a body is either at rest or is moving with a constant velocity.
If the clockwise moments and anticlockwise moments are not equal, there will be a turning effect and the object will rotate.

Levers work based on the principle of moments. A lever is a rigid bar or beam that is free to rotate around a fixed pivot point.
The pivot point of the lever is known as the fulcrum. Just balancing a beam about a point demonstrates the power of using a lever.
The -effort arm- is the distance from the effort (the force you apply) to the fulcrum, and the -load arm- is the distance from the fulcrum to the load (the force you wish to overcome or move).
Increasing the length of the effort arm decreases the amount of effort needed to overcome the load. This is a practical application of the principle of moments.

The centre of mass of an object is the point where it can be considered as being concentrated. If freely suspended, an object will come to rest with its centre of mass directly beneath the point of suspension.
The lower the centre of mass of an object, the more stable it is. The stability can also increase by increasing the area of the base of an object.