Thus far, our study of motion has focused on the particle model, in which an object is represented as a mass at a single point in space. As we expand our study of motion to rotation, we need to consider extended objects whose size and shape do matter. Thus this chapter will be based on the rigid-body model:

MODEL 12.1 Rigid-body model

A rigid body is an extended object whose size and shape do not change as it moves.

• Particle-like atoms are held together by rigid massless rods.

• A rigid body cannot be stretched, compressed, or deformed. All points on the body have the same angular velocity and angular acceleration.

• Limitations: Model fails if an object changes shape or is deformed.

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Workbook Exercise 1

FIGURE 12.1 illustrates the three basic types of motion of a rigid body: translational motion, rotational motion, and combination motion.

FIGURE 12.1 Three basic types of motion of a rigid body.