Chapter 13

Extended Objects

In much of this book, we have focused on the motion of particles. In this chapter, we will explore the physics governing the motion of extended objects. This topic is important for obvious reasons: objects in everyday life are extended in space and have all sorts of shapes, sizes and behavior. To model the motion of extended objects, we need to cover some additional physics and methods. This is a big subject that could easily have filled several chapters, or even a whole book. We have therefore been selective in our coverage, focusing on two topics that we can cover in sufficient depth to provide a good introduction, instead of giving a wider but more superficial presentation.

Topics covered in this chapter include these:

• Rigid bodies: A rigid body is an extended object with a fixed shape and size. In addition to changing its position, such an object can also rotate to change its orientation. We will cover rigid body dynamics, rolling, and rigid body collisions, and illustrate them with a number of different examples.
• Deformable bodies: Objects such as ropes and clothes can change their shapes. We can model such deformable bodies by means of mass-spring systems, building upon the principles discussed in Chapter 8.

Most of the chapter is devoted to rigid bodies, with a much shorter section on deformable bodies.