Key points: - centre of mass is the point at which a single force on the body has no
turning effect
- forces to produce a turning effect the the force applied perpendicular
clockwise and anticlockwise need to be perpendicular and to be in
equilibrium the must be balanced
- the turning effect can be increased if the force applied is greater or if
the distance from the pivot is greater
- a **couple** is pair of equal and opposite forces
