# Momentum and Impulse

Announcements Extra Credit Extra Credit for this six weeks Create an egg basket that can be dropped from 15 feet and will not crack or break. Write a three paragraph paper that explains the physics concepts that goes along with it. Vocab that must be included is:

Collision Velocity Impact Terminal speed - Force - Motion - Momentum

- Kinetic and Potential energy Announcements Extra Credit When will this project be submitted? The Tuesday before Thanksgiving What will it be worth? Replace a minor grade Or up to 20 points on a major grade

Announcements Only 4 weeks left before finals! Watch your grades, this six weeks will go fast. Your next exam will be Tuesday Nov. 18th. You have until this Thursday to correct your work, power, and energy exam. Momentum and Impulse

Lets start with everyday language What do you say when a sports team is on a roll? They may not have the lead but they may have ___________ MOMENTUM A team that has momentum is hard to stop.

What is Momentum? Momentum an object that is hard to stop Momentum = p = mv Units: kgm/s m=mass v=velocity Momentum is also a vector (it has direction) Lets practice A 1200 kg car drives west at 25 m/s for 3

hours. What is the cars momentum? Identify the variables: 1200 kg = mass -25m/s = velocity 3 hours = time P = mv = 1200 x -25 = -30000 kg m/s How hard is it to stop a moving object? To stop an object, we have to apply a

force over a period of time. This is called Impulse Impulse = Ft Units: Ns F = force (N) t = time elapsed (s)

How hard is it to stop a moving object? Using Newtons 2nd Law we get Ft= mv Which means Impulse = change in momentum Why does an egg break or not

break? An egg dropped on a tile floor breaks, but an egg dropped on a pillow does not. Why? Ft= mv In both cases, m and v are the same. If t goes up, what happens to F, the force? Right! Force goes down. When dropped on a pillow, the egg starts to slow down as soon as it touches it. A pillow increases the time the egg

takes to stops. Practice Problem A 57 gram tennis ball falls on a tile floor. The ball changes velocity from -1.2 m/s to +1.2 m/s in 0.02 s. What is the average force on the ball? Identify the variables: Mass = 57 g = 0.057 kg velocity = +1.2 (-1.2) = 2.4 m/s Time = 0.02 s

using Ft= mv F x (0.02 s) = (0.057 kg)(2.4 m/s) F= 6.8 N Car Crash Would you rather be in a head on collision with an identical car, traveling at the same speed as you, or

a brick wall? Assume in both situations you come to a complete stop. Take a guess http://techdigestuk.typepad.com/photos/uncategorized/car_crash.JPG Car Crash (cont.) Everyone should vote now Raise one finger if you think

it is better to hit another car, two if its better to hit a wall and three if it doesnt matter. And the answer is.. Car Crash (cont.) The answer is It Does Not Matter! Look at Ft= mv

In both situations, t, m, and v are the same! The time it takes you to stop depends on your car, m is the mass of your car, and v depends on how fast you were initially traveling. Assignment

Answer questions 2-5 on page 261.

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