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.