Page "Coriolis effect" Paragraph 0

In the inertial frame of reference ( upper part of the picture ), the black object moves in a straight line, without significant friction with the disc.

However, the observer ( red dot ) who is standing in the rotating ( non-inertial ) frame of reference ( lower part of the picture ) sees the object as following a curved path due to the Coriolis and centrifugal forces present in this frame.