Rotating Frame of Reference (Centrifugal force and Coriolis force)




Motions observed in a rotating frame of reference can be accounted for by Newton's second law only when pseudoforces including centrifugal and Coriolis are introduced.

Please read a short note on a very brief outline of these two pseudoforces.


In the left of the applet, the lower plane is the stationary "ground" and the upper one is a rotating frame. These two planes are parallel. The rotating frame rotates counter-clockwise with its axis of rotation passing through the origin of the ground coordinates.

A red ball moves on the ground according to the type of motion chosen, the locus of its projected image on the rotating frame is depicted on the right of the applet.

The motion relative to ground will start a few seconds after the Button "Start" is pressed. This enables us to realize the final motion observed in the rotating frame is a combination of two parts: the rotation of the frame and the motion of the ball itself.


Among the options of the motion relative to ground, the "Linear motion" and the "Linear motion (Coriolis deflection)" may confuse you.

"Linear motion" - the velocity of the red ball (relative to ground) is only the blue arrow.

Linear motion (Coriolis deflection)"- besides the blue arrow, the red ball also takes the tangential velocity of the rotating frame as its initial velocity. This case simulates one sitting on a rotating platform, e.g. merry-go-round, throws an object horizontally to the other side of the platform (the object rotates together with the platform before the throw). If the angular velocity vector of the rotating frame is out of page, the deflection of the object during its flight is always to the right. This effect is well-known because it explains the counter-clockwise circulation of cyclones in the Northern Hemisphere (clockwise in Southern Hemisphere).


When "Linear motion" is selected, a blue circle appears on the ground coordinates. This circle is used to show the magnitude of the linear velocity, i.e. magnitude of velocity of ball = angular velocity of rotating frame x radius of the blue circle.