# PHYS 2211 Module 9.3

## Conservation of Linear Momentum

9.3 Conservation of Linear Momentum

### Learning Objectives

By the end of this section, you will be able to:

• Explain the meaning of “conservation of momentum”
• Correctly identify if a system is, or is not, closed
• Define a system whose momentum is conserved
• Mathematically express conservation of momentum for a given system
• Calculate an unknown quantity using conservation of momentum

### Conservation of Linear Momentum

Discuss!

Consider how you would answer these questions. Then bring this to class for a group discussion.

The red ball in the diagram is chasing after the blue ball; they have the same mass. The speed of the red ball is 3 m/s and the speed of the blue ball is 2 m/s. After the collision the red ball rebounds at 2 m/s and the blue ball speeds away at 3 m/s.

(a) What was the change in velocity experienced by the red ball during the collision?

(b) What was the change in velocity experienced by the blue ball during the collision?

(c) Normally, momentum is conserved during a collision. However if a huge external force acts during the collision, it may not be. Was momentum conserved during this collision or not?

Practice!

Momentum is conserved in this collision since the contact force between Max and Maya during the collision is internal to the system of colliding objects.

Momentum is conserved in this collision since the contact force between the snowball and Maya during the collision is internal to the system of colliding objects.

Momentum is conserved in this explosion since the contact force between the snowball and Maya during the explosion is internal to the system of objects.