**Momentum**

**Momentum**

__Reading__

BJU book: Ch. 11 "Momentum"

__Topics__

Momentum = mass in motion

Typical problems involving elastic and inelastic collisions

Below: "Conservation of Momentum" as illustrated by the collision of two objects at a picnic

Far below: The same principle illustrated by cannon and projectile

Far below: The same principle illustrated by cannon and projectile

__Lecture outline__

Momentum is "mass x velocity" (p = mv).

Thus, it can be thought of as "mass in motion".

We use the letter "p", because the Latin word 'petere' means "to go to", "to attack". It's where we get the words "impetuous, petulant, and impetus"

"Impulse" is a concept Newton came up with to develop his 2nd Law of Motion. We normally write the 2nd Law as "F=ma", but Newton originally expressed it using impulse, as in "Impulse = Change in momentum = force x elapsed time".

From that, you can also say "Impulse = Change in momentum = mass x change in velocity".

Here's a handy chart, below:

__Collisions__

Many homework problems from this chapter are dealing with "collisions".

Rule #1: Total momentum is conserved in all types of collisions. "Conserved" means "doesn't change".

Rule #2: In an "elastic" collision (perfect billiard balls), both Kinetic Energy

__and__momentum are conserved.

Rule #3: In an "inelastic" collision (billiard balls covered with Velcro), only momentum is conserved. Kinetic Energy is not.

__Lab__

"Collision Lab"

__Homework__

8.linear_momentum_homework__problems.docx |