Research Papers in Physics and Astronomy

 

Date of this Version

2020

Citation

Am. J. Phys. 88 (9), September 2020, pp 704-710; http://aapt.org/ajp

doi:10.1119/10.0001388

Comments

Copyright 2020 American Association of Physics Teachers.

Abstract

An American football is a rotationally symmetric object, which, when well-thrown, spins rapidly around its symmetry axis. In the absence of aerodynamic effects, the football would be a torque-free gyroscope and the symmetry/spin axis would remain pointing in a fixed direction in space as the football moved on its parabolic path. When a pass is well-thrown through the atmosphere, however, the symmetry axis remains—at least approximately—tangent to the path of motion. The rotation of the symmetry axis must be due to aerodynamic torque; yet, that torque, at first glance, would seem to have precisely the opposite effect. Here, we explain the action of aerodynamics on the ball’s orientation at second glance.

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