Centrifugal effect

This simulation forms part of a pair of rotation effect physlets. The other rotation effect physlet is the Coriolis effect physlet.

Also available: a 3D simulation (Java applet), called great circles, which presents the rotation-of-Earth effect that is essentially the same as the rotation effect in this simulation.

This simulation represents the case of an object sliding frictionless over the surface of a flat disk that is rotating. I will call the object 'the puck', as in ice hockey. The 'Distance' in the simulation is the distance to the disk's rotation axis. The 'Velocity' is relative to the disk; 0.3 velocity means that at the instant of being launched the puck's velocity relative to the disk is 30 % of its co-rotating velocity at that particular distance to the rotation axis. That is, close to the rotation axis 0.3 represents a slower velocity than close to the disk's rim.

The disk supports the weight of the puck, but since there is no friction the rotation of the disk does not affect the motion of the puck. So there's no dynamics going on; there is no exchange of momentum, no change of kinetic energy.

Evolution of the simulation

The simulation starts in mid-motion. You must think of the disk as already rotating before the simulation is started. The puck is initially co-rotating with the disk, and at some point in time the puck is released. The simulation cuts in at the point of release. The puck is launched in a direction that is tangent to a concentric circle, and from then on it moves along a straight line, with uniform velocity.

The puck can be launched forward and backward, or it can be released without a velocity relative to the point it is released from. Before release/launch the puck already has a velocity, it's co-rotating with the disk. A forward launch increases that velocity. Note that a backward launch does not reverse the puck's velocity, the launch is backward relative to the disk; after the launch the puck is still moving in the same direction, but slower than before. (Of course, if you would launch backward hard enough you would reverse the velocity, but in this simulation that possibility is not included.)

Both when launched forward and when launched backward the puck proceeds away from the rotation axis of the disk. There is no centripetal force, so the puck is always going to flee away from the center.

The version centrifugal effect 2 launches two objects simultaneously, one forward and one backward.

I refer to this rotation effect as 'centrifugal effect': the puck is always going to flee away from the center. It's important to note the contrast with the Coriolis effect. The distinguishing feature of the Coriolis effect is that the acceleration with respect to the rotating system is the same for any direction of velocity relative to the rotating system. In the above centrifugal effect simulation you see that when the puck is launched backward it moves in a direction away from the rotation axis, whereas in the case of the Coriolis effect an object that moves backward (with respect to the rotating system) will move closer to the central axis of rotation

Of course, as the puck moves away from the center of the rotating disk the difference in velocity between the puck and the part of the disk where it is located becomes larger and larger. The velocity of the puck remains the same, but the parts of the disk far away from the center have a larger velocity, so the velocity of the puck relative to the disk keeps increasing. The Coriolis vector is proportional to the velocity relative to the rotating system and pretty soon the Coriolis vector is larger than the centrifugal vector. But it's still not the Coriolis effect, for the puck still keeps moving away from the disk's rotation axis.

Motion in a straight line

Summerizing: the centrifugal effect is a consequence of the fact that the puck is moving in a straight line.

Rotation-of-Earth effect

As mentioned at the start of this article, you can also try the following 3D simulation, called Great circles, which presents the rotation-of-Earth effect that is analogous to the rotation effect in this simulation.

The physlet simulation environment has been created by Davidson College.

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Last time this page was modified: July 17 2010