# Forces and Motion: Principle of Moments

## Forces and Motion: Principle of Moments

• The principle of moments explains the turning effect produced by a force.
• It states that for an object to be in equilibrium (not turning), the sum of the clockwork moments must equal the sum of the anti-clockwise moments.
• A moment is calculated by multiplying the force applied by the perpendicular distance from the pivot point to the line of action of the force.
• The unit of moment is Newton-metre (Nm).
• Increasing the force or the distance from the pivot will increase the moment.
• Examining leverage, a smaller force can have a greater moment if its distance from the pivot is larger.
• Centre of mass is the point where weight can be considered as acting.
• If freely suspended, an object will come to rest with its centre of mass directly beneath the point of suspension.
• If an object is balanced on a point, that point must be vertically below the centre of mass.
• The stability of an object is affected by the position of its centre of mass; a lower centre of mass tends to make an object more stable.
• Knowledge of the principle of moments is useful for understanding how tools such as levers and gears work.
• Forces have both magnitude and direction, making them vector quantities. Both of these will affect the resultant moment on an object.