Hands-On, Minds-On Meteorology
Description | Programming | Operation

Coriolis (including large-sized version)


The Coriolis program is designed to replicate the merry-go-round animation found on the WW2010 website, but to provide an interactive platform for students to investigate. The program shows a rotating disc that has the capability to spin in both directions The action can be viewed from outside the rotational frame of reference, or from within the rotational frame of reference. A larger version for use in lecture halls is also available.

click for whole shot



The primary objective of the Coriolis program is to provide students the means by which to discover how and why the Coriolis effect works.




The program begins with the ball at the edge of a stopped disc. Once the student begins to spin the disc, he or she can release the ball towards the middle. If you are looking at the disc from above, you are not rotating along with it, the ball has not only the original radial (towards the center) velocity, but it also has the rotational velocity of the disc. The ball will travel straight along the path that sums these two velocity components, while the disc is rotating underneath. In the Above Disc case, two paths are drawn, the red path illustrates the ball as it moves, and is always straight. The black path represents where the ball was on the disc at the time it passed, like there was black paint on the ball marking its path on the disc. This path will always be curved unless the disc's rotation is 0. In the On Disc case, only a black path, showing the balls movement is drawn.


The ball is always initially thrown towards the center of the disc with respect to the release point.


Note that no equation for Coriolis force is actually used to display any of the paths. An earlier version of the program did use Coriolis force equations to determine the path in the On Disc case, but two many assumptions are made in the equations that cause increasing error with respect to the Above Disc case. The paths grew increasingly different as rotation speeds increased so they had to be removed. Instead the black path from the Above Disc. case is simply drawn without rotating it. Deflection measurements are calculated by determining how far the ball is from the centerline axis (seen most easily in On Disc. mode).


Any other information



Running the Program

  • Click the link for Coriolis or Coriolis (Large).
  • Initial Radial Speed changes the speed the ball is initially released at.
  • Rotation (rpm) changes the rate at which the disc rotates. A negative rotation rate causes the disc to rotate counterclockwise -- or in the opposite direction when the rotation (rpm) is positive.
  • Once the desired values are set, start the disc by clicking the Start button.
  • When ready, release the ball by clicking the Release button.
  • Press the Stop button to stop the disc.
  • At any time, change the viewing perspective by clicking the appropriate radio buttons.
  • Pressing Start again resets the experiment and deletes existing data.

Extra Knowledge



Department of Atmospheric Sciences
University of Illinois at Urbana Champaign

Created by Dan Bramer: Last Modified 07/27/2004
send questions/comments to bramer@atmos.uiuc.edu