A spinning ice-skater who speeds up when she pulls in her arms is a common textbook illustration of how changing a rotating object’s moment of inertia affects its angular speed. An analogous classroom demonstration involves sitting on a rotating stool while moving handheld weights in and out. Given that students have difficulties understanding conservation of angular momentum when the moment of inertia changes,1 we wanted to add a quantitative experiment that closely resembled the typical textbook example and the in-class demonstration. A few such experiments have been published: an apparatus that moves masses radially relative to a person rotating on a stool,2 a rotating track along which model cars move radially inward or outward,3 and a modified, centripetal-force apparatus with masses that slide outward.4 The first two were more elaborate than we wanted, but the third one seemed to be a suitable experiment for an introductory...

Supplementary Material

AAPT members receive access to The Physics Teacher and the American Journal of Physics as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.