Physics, Chapter 11: Rotational Motion (The Dynamics of a Rigid Body)

Authors

• Henry Semat, City College of New York
• Robert Katz, University of Nebraska-LincolnFollow

Document Type

Article

Date of this Version

1-1958

Comments

Published in Physics, by Henry Semat and Robert Katz, New York: Rinehart & Company, Inc., 1958. Copyright © 1958 Henry Semat and Robert Katz. All rights reserved. Used by permission.

Abstract

The motion of the flywheel of an engine and of a pulley on its axle are examples of an important type of motion of a rigid body, that of the motion of rotation about a fixed axis. Consider the motion of a uniform disk rotating about a fixed axis passing through its center of gravity C perpendicular to the face of the disk, as shown in Figure 11-1. The motion of this disk may be described in terms of the motions of each of its individual particles, but a better way to describe the motion is in terms of the angle through which the disk rotates. Calling two successive positions of a point in the plane of the disk P₁ and P₂ , we find the angle of rotation by drawing radial lines from C to P₁ and to P₂ . The angle Ө between these two lines is the angle through which the disk has rotated; every point in the plane of the disk has rotated through the same angle Ө in the same interval of time. The angle Ө is called the angular displacement of the body. Both the angle Ө and the direction of the axis of rotation must be given in order to specify properly a rotational displacement.