Coriolis

From GeoMod

Demo of the model.

A VPython model of a marble that can be fired across a rotating turntable. The trail of the marble's path across the turntable is traced behind it to show the Coriolis Effect. An application of the model in a large lecture class is described in the paper by Urbano and Houghton (2006).

• There are links to excellent descriptions of what exactly is the coriolis effect (eg. Teunissen, 2007) and some of its history in the coriolis links section below.

Black and white rendering (for publication) of the coriolis effect as viewed from the perspective of the marble fired at the “Target". Since the turntable is rotating, the marble will miss the intended target.

Download software

Multimedia

• Simple animated gif showing the effect
• Media:coriolis_demo.gif: Demo showing ball's point-of-view.
• Coriolis-perspective_shot.mov: Quicktime .mov showing be ball's point of view (16 Mb)

About

Like a number of 2-D Javascript applications available on the web, this model allows the user to fire a ball across a rotating disk, and marks its position relative to the disk and the general co-ordinate system. In this VPython model the user can also control the velocity of the ball, the angular velocity of the disk and the friction between the ball and the disk. This model is particularly useful in illustrating the effect of coriolis on atmospheric motion where these three parameters interact. A target can be placed on the disk to offer an objective of shooting the ball and to illustrate angular velocity. The model also permits the user to view the scene from the perspective of the ball, which has proven to be an extremely popular feature for all ages. This model and its application in a large lecture is described in Urbano and Houghton (2006).

• NOTE: This model only accounts for the conservation of angular momentum component of the coriolis effect and not for conservation of linear momentum, which results in only half of the coriolis force (see Persson, 1998 for a good explanation).

Rotating disk viewed from above.

User's Guide: Model Controls

Cannon

Close view of cannon

1. Fire the marble by clicking on the marble atop the cannon.
2. Drag the cannon by its barrel to any position in the scene
3. Retreive the marble by clicking on the box (loader) of the cannon. (This leaves the marble trail on the turntable.)

Sliders

1. Velocity: Sets the speed of the marble.
2. Rotation: Sets the angular velocity and direction of rotation of the turntable.
3. Friction: Sets the degree of friction between the marble and the turntable.

Balls and buttons

1. Target: Rotates with the turntable when it is dragged onto the turntable. (Great for explaining angular velocity)
2. Reset All: Retreives the marble to the turntable and clears all trails off the turntable
3. Unmarked in the upper right: When this button is clicked it turns red and you see the scene from the marble's point of view. (Kids love this.)

References

• Urbano, L., and Houghton, J., 2006. An Interactive Computer Model for Coriolis Demonstrations, Journal of Geoscience Education, v. 54, no. 1, p. 54-60. (preprint)
  • describes the application of the model in a large lecture class

Notes

1. Friction here only acts to drag the marble with the rotating turntable, and does not slow the marble speed (except if the rotation is moving the marble backward on the turntable).
2. This model only accounts for the conservation of angular momentum component of the coriolis effect, which gives only half of the effective coriolis force (see Persson, 1998).

Coriolis Links

There are a number of other sites that have excellent explanations of the coriolis effect, weather you need a simple description or a more in-depth analysis of the math. I've linked a subset of these below.

Explanations of the coriolis effect

• Articles/webpages by Cleon Teunissen that give a good in-depth explanation of the coriolis effect (with great animations and diagrams).
  • Physlets showing
    • The coriolis effect: http://www.cleonis.nl/physics/physlets/coriolis_effect.html
    • The centrifugal effect: http://www.cleonis.nl/physics/physlets/centrifugal_effect.html
  • The Eötvös effect, which like the coriolis effect is a result of relative motions on the rotating earth.
  • For the best in-depth explanation of the coriolis effect, view the series of interconnected articles:
    1. Rotational-vibrational coupling; the mathematical derivation and nice animations showing rotational-vibrational coupling viewed from static versus rotational co-ordinate systems.
    2. Inertial oscillations (meteorology); description with key mathematical and conceptual models.
    3. Comparison of inertial oscillations and ballistics: Excellent explanation of the coriolis effect and deflection of a puck on a rotating disk (like this coriolis model) and on a sphere
    4. Cyclonic flow: Puts everything in the context of cyclonic flow.

History and explanations of the coriolis effect

• An excellent history of the coriolis effect (pdf) by Anders Persson (Persson, 2005).
• Note also the excellent history of Gaspar Gustave Coriolis included in Dr. Persson's article on How Do We Understand the Coriolis Force? (pdf). This article also has a great explanation of the effect itself.
• Persson also has another good paper with explanation of the coriolis effect in the context of its history called The Coriolis Effect – a conflict between common sense and mathematics
• Persson also has a very good article on Hadley’s Principle: Understanding and Misunderstanding the Trade Winds.