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ERIC Number: EJ1155514
Record Type: Journal
Publication Date: 2017-Oct
Pages: 4
Abstractor: As Provided
ISSN: ISSN-0031-921X
Stable and Unstable Rotational Dynamics of a Smartphone
Loth, Matthew; Gibbons, Chad; Belaiter, Sami; Clarage, James B.
Physics Teacher, v55 n7 p431-434 Oct 2017
One of the canonical, and memorable, classroom demonstrations from an upper-division mechanics course is to toss a rigid body with three distinct principal moments of inertia into the air, giving it a spin along one of its three principal axes. A student's mechanics textbook itself works great for the body, secured rigidly shut with a rubber band. The book will spin stably about its longest and shortest dimensions, just like a top or gyroscope. What is surprising is that any attempt to spin the book about its intermediate axis (the axis parallel to the book's lines of text) will result in a wildly unstable and chaotic tumbling, which most students find curious enough to warrant staying awake for a subsequent derivation of Euler's equations. However, now that most students read their text "books" off of a tablet or phone, this demonstration may seem outdated. Or is it? Like a textbook, a phone or tablet also has three distinct principal moments. Better still, not only do these solid state devices require no rubber band, but these bodies can collect detailed data on their dynamical state, turning a demonstration into an actual experiment. This article reports the results of this modern version of the classical "book toss" demonstration, fittingly carried out by a team composed of both an old physics professor and a youthful group of three undergraduate students studying physics and engineering.
American Association of Physics Teachers. One Physics Ellipse, College Park, MD 20740. Tel: 301-209-3300; Fax: 301-209-0845; e-mail:; Web site:
Publication Type: Journal Articles; Reports - Research
Education Level: Higher Education
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A
Grant or Contract Numbers: N/A