UNDERSTANDING COLLISIONS

To improve the safety of cars, the motion of a car during a crash must be understood and the forces on the driver minimised (Figure 6.1). In this way, safer cars have been developed and many lives have been saved. Find out about as many safety features of cars as you can and discuss with someone else why these features improve safety in a crash.
In this chapter, we will explore how the idea of momentum can allow us to predict how objects move after colliding (interacting) with each other. We will also see how Newton’s laws of motion can be expressed in terms of momentum.

Snooker players can perform some amazing moves on the table, without necessarily knowing Newton’s laws of motion – see Figure 6.2.

However, the laws of physics can help us to understand what happens when two snooker balls collide or when one bounces off the side cushion of the table.
Here are some examples of situations involving collisions:
- Two cars collide head-on.
- A fast-moving car runs into the back of a slower car in front.
- A footballer runs into an opponent.
- A hockey stick strikes a ball.
- A comet or an asteroid collides with a planet as it orbits the Sun.
- The atoms of the air collide constantly with each other, and with the walls of their surroundings.
- Electrons that form an electric current collide with the vibrating ions that make up a metal wire.
- Two distant galaxies collide over millions of years.
From these examples, we can see that collisions are happening all around us, all the time. They happen on the microscopic scale of atoms and electrons, they happen in our everyday world, and they also happen on the cosmic scale of our Universe.