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?

Brainstorming What 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

Momentum 1/3/11 LAST 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

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

Example: Stopping a vehicle A 2200 kg SUV traveling at 94 km/h (26 m/s) can be stopped in a. 21 s by gently applying the brakes b. 5.5 s in a panic stop c s if it hits a concrete wall Find 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 Momentum 1/4/11: Inelastic Collisions

Systems: Closed system: a system which does not gain or lose mass Isolated 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

Types of Collisions: Elastic: objects do not stick together after collisions Inelastic: objects stick together after collision a/momentum/creti.cfm a/momentum/creti.cfm

Inelastic Collision Objects sticking together after collision will have the same velocity: Take a collision between two objects (m 1 and m 2 ). 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 Collisions Objects do not stick together; the objects do not have the same final velocity

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 Collisions 1/5/11

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 v i are 0)

Examples of recoil: Explosion A diver shooting a gun in the water Ice skaters pushing one another An 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 homework 2. Your notecard for your quiz tomorrow 3. 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: Homework In 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 + V i =26 m/sV f =0 m/s

Steps: List Knowns and Unknowns: Knowns: m=2200 kg v i =26 m/s v f =0 m/s ∆t=21s, 5.5s, 0.22s Unknowns: F=?

Steps: Calculation Determine the momentum before and after Apply impulse-momentum theorem to calculate force