GCSE Physics - The Turning Effect of Forces

Forces can have a turning effect or moment on a body

Moment of a force = force x perpendicular distance to the pivot

When an object is balanced:

sum of anti-clockwise acting moments = sum of clockwise acting moments

Centre of gravity - the point where a object will balance on a pivot. The whole weight of the object appears to act at this point.

For a regular shape, the centre of gravity is where the lines of symmetry cross.

For an irregular shape, the centre of gravity is found by hanging the shape by a pivot and hanging a plumb line at the same place. A line can be drawn along where the plumb line hangs. Repeat this again in a different place and the centre of gravity is were the two lines cross.

Stable objects have low centres of gravity and wide bases

When a heavy object is resting on a beam, the upward forces at the ends of the beam depend onthe position of the object.