 And if you cancel out the fetus and move the V up to the top, we get that the acceleration, A, is equal to the velocity B squared, divided by R, the radius. We have now found the magnitude of the acceleration of an object undergoing uniform circular motion, also known as the centripetal acceleration. But we know that acceleration is a vector, so what about the direction? Well, the key fact to remember here is that the speed is constant. Now this means that there can't be any component of acceleration that is in the same direction as the velocity, otherwise the speed would change. We know from our previous velocity derivation that the velocity always points tangentially to the circle. This must mean that all of the acceleration must be perpendicular to the tangent, which is in the radial direction. The final bit we need to do is to figure out whether this acceleration is pointing radially inwards or radially outwards. Now, we know that the acceleration must be in the same direction as delta V, our change in velocity. So if we draw out a triangle with V1, V2 and delta V, it's clear that delta V is pointing in towards the centre of the circle and not away from the centre of the circle. This means that the acceleration must point radially inwards. And there we have it. The acceleration of an object undergoing uniform circular motion is V squared on R and it points radially inwards. This is called the centripetal acceleration.