In short, you're pushing the ball around, and the force you use depends on three things: - how far the ball is from the target (P, proportional) - how far the

In short, you're pushing the ball around, and the force you use depends on three things: - how far the ball is from the target (P, proportional) - how far the ball has been from the target over time (I, integrator), so if you are very far even after a long time you try to push harder - how quickly is the ball approaching the target (D, derivator), i.e. if you're approaching quickly then you decrease the force, if you're approaching too slow then you increase the force