Driving forces of plate tectonics and the importance of inertia

Donald Forsyth
,
Brown University
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Summary

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

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Context

Audience

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

None

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

Goals

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

None

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.

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