IG Phy – Moments of Force

The turning effect of a force is called the moment of the force.

The moment of a force depends on the size of the force and the perpendicular distance from the pivot.

If the perpendicular distance from the pivot is increased, the moment of the force is decreased.

Moment is measured in newton meters (Nm) or newton centimeters (Ncm).

The principle of moments states that the sum of the clockwise moments equals the sum of the anticlockwise moments about any point if the system is not turning.

In a balanced see-saw, the clockwise and anticlockwise moments are not equal.

The moment equation is given by moment = force × perpendicular distance from the pivot.

Amy pushing a door with a force of 20 N at a distance of 0.80 m from the hinges results in a moment of 16 Nm.

If Phil causes an anticlockwise moment of W × 2.0 m and Tom causes a clockwise moment of 400 N × 3.0 m, then W is 600 N.

For a system to be in equilibrium, there must be a resultant force and a resultant turning effect.

The principle of moments can only be applied to systems with a single force acting on each side of the pivot.

In the worked example of the meter rule, the sum of clockwise moments is equal to the sum of anticlockwise moments.

The tension in the spring in the meter rule example is calculated to be 7.3 N.

An experiment to verify the principle of moments involves drilling a hole at the 50 cm mark of a meter ruler.