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# Conservation of Momentum

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Notes from Ms. Parker's class Feb 11 & 14

Notes from Ms. Parker's class Feb 11 & 14

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### Transcript

• 1. Good Afternoon!
Today we will:
finish our investigation
take some notes
solve some momentum problems
get out your lab notebook and pen/pencil
find the lab we started Wednesday
open your textbook to pg 310
• 2. Conservation of Momentum
• 3. Warm-Up
On your whiteboard, solve the following problem. SHOW GUTS!
What is the momentum of a 0.3 kg cart moving at a velocity of 0.5 m/s?
• 4. Warm-Up #2
Identify the independent variable:
What is the effect of increasing mass on objects with a constant momentum?
Identify the dependent variable: (it’s NOT momentum)
• 5. Pre-Lab
You are looking for:
materials
data you will be recording
3 minutes
• 6. Lab: Conservation of Momentum
Open your lab book to the nearest clean page and title this lab, “Conservation of Momentum.”
• 7. Lab: Conservation of Momentum
Groups of 5 – 6
Everyone writes down all data and answers in their lab book DURING the lab
We will do Steps #1 – 3 in our lab
• 8. Lab: Conservation of Momentum
In your lab book, identify the independent and dependent variable
On your whiteboard, write an “if, then, because” hypothesis.
Write a hypothesis in your lab book.
• 9. Data Table
Following the directions on page 311, #1a, create a data table in your lab book that looks like the textbook’s. We will do SIX collisions.
PLUS:
Create the data table you see on page 311, #3a.
How many entries will this data table have?
8 minutes
• 10. Review Momentum
Bill Nye
• 11. Conservation of Momentum
Momentum, like energy, is conserved.
What does this mean for a car crash?
In a car crash, if you add up all the momentum before a collision, it will equal the total momentum after a collision.
Momentum BEFORE collision = Momentum AFTER collision
• 12. Conservation of Momentum
Of course, there is a formula
m1v1 + m2v2 = (m1 + m2)vf
momentum before = momentum after
Why do we add the masses together after the collision?
because they stuck together and travel at the same speed
collisions in which the two objects stick to each other are called inelastic collisions
• 13. Conservation of Momentum
The conservation of momentum is true whether or not the objects “stick” together, however so the better (more generic, applies to all situations) formula might be:
m1v1b + m2v2b = m1v1a + m2v2a
Momentum Before = Momentum After
collisions in which the objects bounce off of each other are called elastic collisions
• 14. Law of Conservation of Momentum
The total momentum beforea collision is equal to the total momentum afterthe collision if no external forces act on the system.
• space station video
this is true for all collisions between any objects!
a car and a truck
a proton and a proton
a planet and a meteor
• 15. Conservation of Momentum
Conservation of momentum is a crucial piece to understanding and predicting motion.
Since we know the total momentum in the beginning of a collision, we know the total momentum after the collision.
We can use this understanding to help us predict the results of any collision.
• 16. Sample Problem #1 pg 314
A 75 kg boy and a 50 kg girl are riding in identical bumper cars at an amusement park. The boy’s car is moving to the east at 3.00 m/s and the girl is moving west at a velocity of 1.80 m/s. If they stick together on collision, what is their final velocity?
• 17. Conservation of Momentum in Elastic Collisions
What if the two objects don’t stick together, but move away in the same direction at different speeds?
What formula should you use?
m1v1b + m2v2b = m1v1a + m2v2a
• 18. Sample Problem #2 pg 315
A steel ball with a mass of 2kg is traveling 3 m/s west. It collides with a stationary ball that has a mass of 1 kg. Upon collision, the smaller ball moves to the west at 4 m/s. What is the velocity of the larger ball?
• 19. Checking In
A vehicle with 6000 kgm/s of momentum collides with a car at rest. As they slide off together, what is their momentum?
• 20. Success Criteria Check (Regular)
P: Using the diagrams and the words “momentum, conservation of momentum, mass, velocity, and direction,” describe how we can predict the motion (speed and direction) of objects after a collision
ADV: A 2 kg cart collides into a 1 kg cart at rest with a velocity of 9 m/s to the left. If the carts stick together, what is their velocity after the crash?
• 21. Success Criteria Check (Honors)
P: Using the diagrams and the words “momentum, conservation of momentum, mass, velocity, and direction,” describe how we can predict the motion (speed and direction) of objects after a collision and give a fictional example using mathematics to illustrate your explanation
ADV: see Ms Parker for Challenge Problem