All Physics Faculty Publications

Document Type


Journal/Book Title/Conference

European Journal of Physics

Author ORCID Identifier

Boyd F. Edwards:

John M. Edwards:






Institute of Physics Publishing Ltd.

Publication Date


Award Number

NSF, Division of Chemistry (CHE) 1808225


NSF, Division of Chemistry (CHE)

First Page


Last Page



We explore the forces that shape our spheroidal Earth and the forces that govern the motion of a puck that slides without friction on its surface. The Earth's stable spheroidal shape (apart from small-scale surface features) is determined by balancing the gravitational forces that hold it together against the centrifugal forces that try to tear it apart. The motion of a puck on its surface differs profoundly from motion on a sphere because the Earth's spheroidal deformations neutralize the centrifugal and gravitational forces on the puck, leaving only the Coriolis force to govern the motion. Yet the Earth's spheroidal deformations are small and difficult to see in scale drawings. To assist students in exploring the crucial role of these deformations for motion on the Earth's surface, we develop a model of uniformly rotating homogeneous earth-like planets with arbitrary eccentricities and arbitrary angular speeds of rotation, derive equations of motion for a puck sliding on the frictionless surface of such a planet, and introduce CorioVis software for visualizing this motion. By construction, this model replicates the rotational properties of the reference spheroid that is used in terrestrial cartography, geodesy, and the global positioning system.


This is the Accepted Manuscript version of an article accepted for publication in European Journal of Physics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at

Included in

Physics Commons