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Conservation of Momentum

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

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Conservation of Momentum

  1. 1. Good Afternoon!<br />Today we will:<br />finish our investigation<br />take some notes<br />solve some momentum problems<br />Please do before the bell:<br />get out your lab notebook and pen/pencil<br />find the lab we started Wednesday<br />open your textbook to pg 310<br />
  2. 2. Conservation of Momentum<br />
  3. 3. Warm-Up<br />On your whiteboard, solve the following problem. SHOW GUTS!<br />What is the momentum of a 0.3 kg cart moving at a velocity of 0.5 m/s?<br />
  4. 4. Warm-Up #2<br />Identify the independent variable:<br />What is the effect of increasing mass on objects with a constant momentum?<br />Identify the dependent variable: (it’s NOT momentum)<br />
  5. 5. Pre-Lab<br />Please read pages 310 – 311<br />You are looking for:<br />materials<br />data you will be recording<br />3 minutes<br />
  6. 6. Lab: Conservation of Momentum<br />Open your lab book to the nearest clean page and title this lab, “Conservation of Momentum.”<br />Be sure to make an entry into your Table of Contents as well.<br />
  7. 7. Lab: Conservation of Momentum<br />Groups of 5 – 6<br />Everyone writes down all data and answers in their lab book DURING the lab<br />We will do Steps #1 – 3 in our lab<br />
  8. 8. Lab: Conservation of Momentum<br />In your lab book, identify the independent and dependent variable<br />On your whiteboard, write an “if, then, because” hypothesis.<br />Write a hypothesis in your lab book.<br />
  9. 9. Data Table<br />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.<br />PLUS: <br />Create the data table you see on page 311, #3a. <br />How many entries will this data table have?<br />8 minutes<br />
  10. 10. Review Momentum<br />Bill Nye<br />
  11. 11. Conservation of Momentum<br />Momentum, like energy, is conserved.<br />What does this mean for a car crash?<br />In a car crash, if you add up all the momentum before a collision, it will equal the total momentum after a collision.<br />Momentum BEFORE collision = Momentum AFTER collision<br />
  12. 12. Conservation of Momentum<br />Of course, there is a formula<br />m1v1 + m2v2 = (m1 + m2)vf<br />momentum before = momentum after<br />Why do we add the masses together after the collision?<br />because they stuck together and travel at the same speed<br />collisions in which the two objects stick to each other are called inelastic collisions<br />
  13. 13. Conservation of Momentum<br />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:<br />m1v1b + m2v2b = m1v1a + m2v2a<br />Momentum Before = Momentum After<br />collisions in which the objects bounce off of each other are called elastic collisions<br />
  14. 14. Law of Conservation of Momentum<br />The total momentum beforea collision is equal to the total momentum afterthe collision if no external forces act on the system.<br /><ul><li>space station video</li></ul>this is true for all collisions between any objects!<br />a car and a truck<br />two railroad cars<br />a proton and a proton<br />a planet and a meteor<br />
  15. 15. Conservation of Momentum<br />Conservation of momentum is a crucial piece to understanding and predicting motion.<br />Since we know the total momentum in the beginning of a collision, we know the total momentum after the collision.<br />We can use this understanding to help us predict the results of any collision.<br />
  16. 16. Sample Problem #1 pg 314<br />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?<br />
  17. 17. Conservation of Momentum in Elastic Collisions<br />What if the two objects don’t stick together, but move away in the same direction at different speeds?<br />What formula should you use?<br />m1v1b + m2v2b = m1v1a + m2v2a<br />
  18. 18. Sample Problem #2 pg 315<br />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?<br />
  19. 19. Checking In<br />A vehicle with 6000 kgm/s of momentum collides with a car at rest. As they slide off together, what is their momentum?<br />
  20. 20. Success Criteria Check (Regular)<br />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<br />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?<br />
  21. 21. Success Criteria Check (Honors)<br />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<br />ADV: see Ms Parker for Challenge Problem<br />

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