If you have ever found yourself hanging on for dear life as you are flung in a circle on a white-knuckle ride at the fairground, it is easy to arrive at the conclusion that there is a force pushing you away from the centre of the circle.But if we analyse the motion of a ball on a string we find that there is only one force acting on the ball and that is towards the centre - not away from it.Even though the ball"s speed...