Momentum

Definitions:

“Momentum is the product of an object’s mass and its velocity.”OR

“Momentum is a measure of how hard it is to stop or turn a moving object.”

The symbol for momentum is: p

The equation is: for “linear momentum”.The units are:

kg for the mass m/s for the velocity

Example 1

• A 2250 kg pickup truck has a velocity of 25 m/s to the east. What is the momentum of the truck?

running girl OR running boy?

What if both of them had the same speed – would that affect your answer?

Which one has more momentum?

A parked car? OR A crawling centipede?

Explain your answer.

Which do you think has more momentum?

Is it possible that they could ever have the same momentum?

For two objects to have the same momentum, they either need:

1. Not the same masses, or the same velocities, but the same mxv.

2. Equal velocities of zero. If they are both at rest then they both have zero momentum.

Sample Problem

How fast must a 2 kg rock be thrown in order to have the same momentum as a 3 kg rock that was thrown at a speed of 8 m/s?

Sample Problem

A 90-kg tackle runs West at 5.0 m/s and a 75-kg quarterback runs East at 8.0 m/s.

a. Who has more momentum?

b. What happens if they collide?

Important point:

Momentum is often used to figure out who will “win” if two things collide.

In a head-on collision, the object with the most momentum will “push” the other object backward.

Sample Problem

How fast must an electron move to have the same momentum as a proton moving at 300 m/s?

(handy fact: the mass of a proton is ~ 2000x greater than an electron)

Just remember:

It’s better to have mo-mentum than it isto have less-mentum!