How can an object be accelerating when it's velocity is constant, and how does centripetal acceleration work.

Although an object in circular motion travelling at constant velocity isn't accelerating in the conventional sense, ie. changing speed, it's important to remember that it is a vector. Vector quantities have both magnitude and direction, and although the magnitude of the velocity isn't changing, it's direction is as it goes round the circle. This change in direction of the velocity is a centripetal acceleration. The force acting on the object towards the centre, from a string for example, is constantly pulling the object radially inwards. The centripetal acceleration can be calculated with the formula: v^2/r, where v=velocity and r=radius of circle. (Derivation of this formula is required and will be carried out in session.)