An Interactive Computer Model for Coriolis Demonstrations

Article excerpt

ABSTRACT

The coriolis effect can be a difficult concept for students to understand, particularly in large classes where the effectiveness of physical demonstrations is limited by visibility. We developed a fully interactive computer visualization aimed at introductory undergraduate and precollege students based on the physical demonstration of a marble rolling across a turntable. The marble's velocity, turntable angular velocity and direction, and friction between the marble and the surface can be controlled to allow significant instructional flexibility. Pre and post demonstration student surveys indicate that the application improved student understanding of the coriolis effect, and the use of this type of demonstration was favorably received by the students. This program is written in the free, open-source Python programming language, specifically with the VPython module, which makes three-dimensional, physically-based, real-time visualizations efficiently programmable for geoscience demonstrations by non-professional programmers.

INTRODUCTION

Wind speed and direction over the surface of the Earth are controlled by the balance among the pressure gradient force, the coriolis effect and friction with the ground. The interaction of these three forces is vital in describing atmospheric motion but can be difficult to convey both individually and in concert. The coriolis effect is the most complex and least intuitive of the three forces because it involves relative motions perceived between two reference frames resulting in a fictitious force. As a result, much effort has been devoted to simplified explanations (e.g., Vandegrift, 1995; Schmidt, 1985), and a number of physical demonstrations have been designed to show this effect in the classroom (such as O'Connell, 2000; Arne, 1982; Levine, 1978).

The most common demonstrations involve moving an object, such as a marble, in a straight line across a rotating disk. Although the object moves in a relatively straight line, its path across the turntable transcribes a curve as the turntable spins out from under it. These demonstrations are, however, difficult to visually project to large lecture classes, leading to the development of a number of variations to address this problem. Arne (1982) suggested using a drop of colored water that leaves a trail as it drips vertically across a tilted rotating disk, while Levine (1978) used a pen to trace straight-line segments on a piece of paper as it is rotated over a discrete angle, creating a type of stop motion animation. Even with these modifications the effectiveness of any physical model is limited by its ability to be seen from the back of an auditorium.

For computer-based lectures, another alternative is to use an animation, a number of which are freely available on the Internet. Dray (1999) provides an excellent directory to many of these. These animations, however, tend to be small in size (eg., only filling one-fourth of the projected screen at 1024 by 768 pixels resolution) and of low resolution to accommodate the current bandwidth limitations of many personal Internet connections, limiting their usefulness in lectures. In addition, separate animations have been developed for each of the three component of atmospheric circulation, so that attempts to demonstrate the force interactions during a single lecture can be difficult. Most of these animations can only demonstrate simple scenarios and lack the flexibility and drama of a model in which fundamental parameters can be manipulated interactively during a live demonstration. Reddy (2005) has produced an excellent interactive Java Applet for coriolis demonstrations but it too is restricted in size and to two dimensions. There have also been some attempts to produce internet-based coriolis games. EOA Scientific Systems (2005), for example, have produced a game using an interactive Flash program, but it too suffers from a substantial degree of abstraction by using a fixed Mercator reference map and a linear progression of challenges. …