Imagine there is a frictionless disk that spins with angular speed w. There is a ball on it that sits motionless at some radius r from the center. Now, switch to the frame of the rotating disk. In this frame the ball should be spinning with speed w * r. Edit: To be clear, the ball is NOT moving in the original, inertial frame. Only in the non inertial frame. Since the ball is undergoing apparent circular motion, the net "force" (fictitous included) should be mv^2/r. The centrifugal force provides this force exactly. However, since in this frame the ball also has some velocity relative to the frame, there is also a Coriolis force that is parallel to the centrifugal. As a result the net forces (fictitious included) cannot be mv^2/r. So how is this possible? At first I thought that the V in the Coriolis force equation must only refer to V in the radial direction. However, wikipedia and other sources said v is simply the total relative velocity. As a result I'm very confused. Maybe if somebody could show an easy derivation (like on this kind of spinning disk for the Coriolis force) it would help my confusion. However, it still wouldn't reconcile this seeming contradiction.