Impulse - momentum

Conservation of Momentum

Collisions

Elastic

Inelastic

2-D Collisions

Center of Mass

Relates: Force, time, and momentum

No outside forces

Momentum you start with, is what you end with

Both KE and Momentum are conserved. BOUNCE

Only momentum is conserved, some KE is "lost", STICK

Can be Elastic or inelastic

Do it by COMPONENTS

find in both X and Y directions, same process

As we begin we need to place this information

somewhere we have been.

So we can make an association with what we have

learned.

Momentum and its relation to force

We call this the impulse momentum theorem.

mv

mv

mv'

mv'

A

A

A

A

A

A

A

B

B

B

B

B

B

B

F

F

A from B

B from A

This equation is the conservation of momentum.

The caveat is that there must be no outside forces.

**Collisions**

Thought process

Thought process

A really light mass collided with a really heavy mass, what would happen if...

The heavy mass was very solid, and the light mass was 'squishy' ?

They were both very solid?

Note, momentum is a vector, what about kinetic energy?

Kinetic energy is conserved if the collision is Elastic

Elastic collisions

Only outside forces are an issue.

Newton's Cradle

Energy going in = energy going out

momentum in = momentum out

Final answer. If you have two masses

one initially moving, other at rest,

and they collide elastically, their final

velocities are:

V = 0

2

i

Elastic

linear

Elastic collisions.

If 2nd mass not initially at rest......

If not elastic --- no good

If not linear --- no good.

Change your coordinate system.

Two billiard balls of equal mass undergo a perfectly elastic head-on collision. If one ball's initial speed was 2.00 m/s and the other was 3.00 m/s what will be their speeds and directions after the collision?

**Here my collision equation**

takes on the following form

takes on the following form

**Because Kinetic energy is not conserved,**

there is a 'loss'

thus my energy equation looks like the above.

there is a 'loss'

thus my energy equation looks like the above.

**Inelastic collisions**

In this type of collision, momentum is still conserved

but the kinetic energy is Not.

In a perfectly inelastic collision, the two objects 'stick'

together after the collision.

These are often modeled by clay, or a ballistic problem.

**The equations we have written for conservation of momentum are vector equations.**

Thus we can write them in their x & y components and be alright.

Thus we can write them in their x & y components and be alright.

**2-D Collisions**

**Demo**

**https://video.byui.edu/media/Collision+demonstration/0_3bil8221/20172242**

**Center of mass**

**Physically we think of it as a balance point,**

and this is probably the easiest way to actually

solve for the center of mass.

If you balance off two directions, the intersection

of those lines, will be the center of mass.

Like wise if you spin something, in the air (no other forces)

it will spin around the center of mass.

and this is probably the easiest way to actually

solve for the center of mass.

If you balance off two directions, the intersection

of those lines, will be the center of mass.

Like wise if you spin something, in the air (no other forces)

it will spin around the center of mass.

Computationally.

I can solve for the center of mass by adding up

all the masses at all the locations, and multiplying

those masses by their distance, and then dividing

that whole sum by the total mass.....

like this:

"Im having a little trouble following the collisions in two dimensions problems. "

"can you clarify how to do a FBD or the equivalent to it for this chapter? specifically collisions in two dimensions. "

"I don't understand the difference between inertia and momentum. "

"I didn't get what an impulse was..."

"Momentum vs kinetic energy in a collision?"

Can you explain the first question on the quiz?

Newton's second law can be written as the change of momentum divided by the change in time