Driving forces of plate tectonics and the importance of inertia

Donald Forsyth
Brown University
Author Profile
Initial Publication Date: July 31, 2007 | Reviewed: November 1, 2012


Simple in class calculations showing that inertia or momentum is completely unimportant in considering the driving forces of plate tectonics

Used this activity? Share your experiences and modifications



This has been used both in introductory physical geology course for general science students and in more advanced course for geology/geophysics concentrators Designed for a geophysics course Designed for an introductory geology course

Skills and concepts that students must have mastered


How the activity is situated in the course

Part of a lecture on plate tectonics, prelude to the concept that forces acting on plates must balance


Content/concepts goals for this activity

Inertial terms or momentum completely unimportant when considering what controls plate motion

Higher order thinking skills goals for this activity

Making simple back-of-the-envelope calculations to test an idea

Other skills goals for this activity


Description of the activity/assignment

To demonstrate how unimportant inertia is in plate tectonic problems, as part of a lecture, we calculate momentum and moment of inertia of both a supertanker and a plate. A supertanker running into a dock will do more than a million times more damage than a plate. This activity addresses student misconceptions and has a small quantitative component.

Determining whether students have met the goals

Concept tested on an exam. Students remember this example for years, demonstrating its effectiveness at getting the concept across.

More information about assessment tools and techniques.

Teaching materials and tips

Other Materials