Do Now:Who was the best teacher you ever

had?What was it about that person and

their class that made an impact on you?

BrainstormingWhat does the word

“momentum” mean to you?What about “impulse?How have you used these two

words in your life?

Do Now (1/3/12):1.What does the word

“momentum” mean to you?2.What about “impulse?3.What was the best thing

about your break?Happy New Year

Momentum1/3/11LAST TOPIC OF THE SEMESTER!!!

Linear Momentum:Linear Momentum: the product of

the mass and velocity of an object; represented by the symbol p (units: kg x m/s); is a vector quantity

mvp

Example:Anquan Boldin has a mass of 130

kg. If he runs east at 35 m/s, what is the magnitude and direction of his momentum?

Example:Anquan Boldin has a mass of 130

kg. If he can run at the same speed as Haloti Ngata, who has a mass of 200 kg, who has the greater momentum?

Impulse-Momentum Theorem:The impulse on an object is

equal to the change in momentum it causes

if

if

pptF

mvmvvmtF

Example: Stopping a vehicleA 2200 kg SUV traveling at 94

km/h (26 m/s) can be stopped in a. 21 s by gently applying the

brakesb. 5.5 s in a panic stopc. 0.22 s if it hits a concrete wallFind the average force exerted in

each case.

Practice:Use the rest of class to work on

“Intro to Momentum.” It is due tomorrow!

#4 = “km/h” should be “m/s”

Do Now (1/4/12):

1. A 2400 kg SUV and a 1300 kg sports car are traveling at the same speed. Which one has the greater momentum?

2. If they are both traveling at 20 m/s, what is the momentum of each?

Pass In:Momentum homework (half-

sheet)Last week’s Do Now’s (if you

haven’t already)Home Alone Extra Credit (if you

haven’t already)

Collisions and Conservation of Momentum1/4/11: Inelastic Collisions

Systems:Closed system: a system which

does not gain or lose massIsolated system: a system with a

net external force equal to zero

The Law of Conservation of Momentum

The momentum of any closed isolated system does not change

fi pp

Types of Collisions:Elastic: objects do not stick

together after collisions Inelastic: objects stick together

after collisionhttp://www.physicsclassroom.co

m/mmedia/momentum/creti.cfm

Inelastic Collision

Objects sticking together after collision will have the same velocity:

fii

ffii

vmmvmvm

vmvmvmvm

)( 212211

212211

fi pp

Take a collision between two objects (m1 and m2). Use Conservation of Momentum:

Example:A 1875 kg car going 23 m/s rear

ends a 1025 kg compact car going 17 m/s on ice in the same direction. The two cars stick together. How fast do the two cars travel together after the collision?

Elastic CollisionsObjects do not stick together; the

objects do not have the same final velocity

ffii vmvmvmvm 22112211

Example: #2 on back of homework:Work with your seatmate to list

the variables in this problem.Determine whether the collision

is elastic or inelastic.

Practice:Use the rest of class to work on

the worksheet “Collisions and Conservation of Momentum.”

Elastic Collisions1/5/11

Do Now:A 1875 kg car going 23 m/s

rear ends a 1025 kg compact car initially at rest on ice in the same direction. The two cars stick together.

1. What type of collision is this?

2. How fast do the two cars travel together after the collision?

Recoil:Both objects start out at rest (both

vi are 0)

ff

ff

ffii

vmvm

vmvm

vmvmvmvm

2211

2211

22112211

0

Examples of recoil: ExplosionA diver shooting a gun in the

waterIce skaters pushing one anotherAn astronaut throwing something

in space

Example:An astronaut at rest in space

fires a thruster pistol that expels 3.5 kg of gas at 875 m/s. The combined mass of the astronaut and the pistol is 84 kg.

How fast and in what direction is the astronaut moving after firing the pistol?

Practice:Please use the rest of class to

work on one of three things:1. Your homework2. Your notecard for your quiz

tomorrow3. Your final materials list (if

needed)

Do Now:Two ice-skaters are at rest on the

ice. The ice skater with a mass of 70 kg pushes 50 kg skater, who recoils with a speed of -12 m/s. How fast and in what direction is the70 kg skater moving?

Classwork:

Please work on one of three things only:

HomeworkIn classroom textbooks: pick 4

problems from each set:◦P. 218: #22-28◦P.219 #34-40

Work on your notecard!

Do Now:

1. What two types of collisions are there?

2. What are the steps for solving momentum problems?

3. Turn in your hw and Do Now’s (you should have six)!!!

Steps: Sketch the Problem Sketch the problem before and after the

event using vectors, including an axis indicating the positive and negative directions

+

Vi=26 m/s Vf=0 m/s

Steps: List Knowns and Unknowns:Knowns:m=2200 kgvi=26 m/s

vf=0 m/s

∆t=21s, 5.5s, 0.22sUnknowns:F=?

Steps: CalculationDetermine the momentum before

and afterApply impulse-momentum

theorem to calculate force