In Chapter 4 we discussed the motion of point particles. However, in our environment the spatial extension of particles in crucial. Physical objects always keep a minimum distance due to their spatial extension. When they had zero extension, one could neither blow up water droplets by impact with a laser (Figure 5.1), nor work clackers (Figure 5.2) or hit a ball with a tennis racket (Figure 5.3). Even giving spin to a ball only works due to the distance between the surface of the racket and the center of the ball.

At the end of this chapter we will be able to discuss the evolution of balls with spin, and their reflections from flat surfaces. Why is spin of so much importance in table tennis? How can a ``Kreisläufer'' score a goal in Handball, even when the goal keeper is fully blocking he direct path to the goal?

• 5.1 Motivation and outline: How do particles collide?
• 5.2 Collisions of hard-ball particles
• 5.3 Volume integrals — A professor falling through Earth
• 5.4 Center of mass and spin of extended objects
• 5.5 Bodies with internal degrees of freedom: Revisiting mobiles
• 5.6 Worked example: Reflection of balls
• 5.7 Problems

The PDF file of the chapter is available here.

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