The subject of centrifugal force comes up at all of our mechanics INSET meetings and it seems that it continues to be a problem when we teach circular motion. Consider the problem of the conical pendulum. The forces acting on the bob are its weight and the tension as shown in Figure 1:

Frequently students put a force outwards in addition to these forces and label it the centrifugal force (or mrω2). It is undeniably true that the lay person (and therefore perhaps all of us at an intuitive level?) feels that this force is there and this is presumably why it appears on force diagrams; after all, it seems quite natural, ‘how else does the bob remain out at an angle if not held by an outwards force?’