next up previous contents
Next: Optics Up: Mechanics. Previous: 2nd Law

3rd Law

The third law is, at first sight, almost unbelievable: if I kick a ball, the ball kicks me back? But in fact it is so: suppose I push a friend while we are both standing on ice (to minimize friction), then he/she will move in the direction of the push, but I will move backward! What happens when I kick a ball is that the push backward is countered by the friction between my other leg and the ground, and because of this no motion backward ensues. It is interesting to do the kick-the-ball experiment on ice, you should try it.



Jose Wudka
9/24/1998