Crumple Zones: Impulse and Momentum


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Crumple Zones: Impulse and Momentum

  1. 1.
  2. 2. Good Morning!<br />Today we will:<br />conduct an investigation<br />take some notes<br />complete a success criteria check<br />Please do before the bell:<br />get your lab notebook<br />get out something to write with<br />get a textbook and open to page 321<br />
  3. 3. What Do You See?<br />
  4. 4. Lab: Crumple Zones<br />Make a new entry in your lab book. Title it, “Impulse and Changes in Momentum: Crumple Zone”<br />Be sure to make the corresponding entry in your Table of Contents<br />
  5. 5. Read pages 321 - 322<br />We will be doing Part A of the lab today. While reading about it, pay special attention to:<br />materials you will use<br />what you will be doing/investigating<br />3 minutes<br />
  6. 6. Crumple Zones<br />What are some of the factors that automobile designers and engineers must consider when designing a crumple zone as a safety feature?<br />1:2:4: Copy this question down in your lab book and jot down your ideas<br />2 minutes<br />
  7. 7. Crumple Zones<br />Share your ideas with your table partner; add anything to your list that you think of while discussing with your partner<br />2 min<br />Now share with the table behind/in front of you<br />2 min<br />
  8. 8. Lab: Crumple Zones<br />In this lab, your group will design what it thinks will be the best crumple zone – you will be given one sheet of paper, 30 cm of tape, 2 rubber bands, and 30 cm of string with which to do so.<br />
  9. 9. Lab: Crumple Zones<br />Set up your ramp, cart, block and books (you can also use the wall) as shown in the picture. Test your set-up to be sure that the car will successfully roll down the ramp and crash into the books/wall.<br />5 minutes<br />
  10. 10. Lab: Crumple Zones<br />In your lab group, discuss, design, and attach your crumple zone to the cart. Your goal: design a crumple zone that will keep the block from tipping over from ramp heights greater than 15 cm.<br />Diagram your design in your lab notebook. Be sure to label your design!<br />12 minutes<br />
  11. 11. Lab Debrief: What works, what doesn’t?<br />The tape doesn’t help hold the block in place when the cart crashes. Why?<br />
  12. 12. Forces Affecting Collisions<br />The goal of a crumple zone is to add “cushioning.” How can we describe cushioning in scientific language?<br /><ul><li>cushioning = increased stopping distance
  13. 13. cushioning = increased stopping time</li></li></ul><li>The Math of Increased Stopping Distance<br />We already know:<br />work done = force x distance<br />work done = ΔKE<br />From these relationships, we get:<br />ΔKE = force x distance<br />We call this the Kinetic Energy – Work Theorem<br />
  14. 14. ΔKE = force x distance<br />Looking at that relationship between the change in kinetic energy, force and distance, keep something in mind:<br />An object in motion has a “set” kinetic energy: it is a factor of its mass and its velocity. To change that kinetic energy, work (force x distance) must be done.<br />
  15. 15. ΔKE = force x distance<br />So, for a given kinetic energy, what happens to force as distance is increased?<br />as distance increases, force decreases<br />
  16. 16. The Math of Increased Stopping Time<br />Instead of focusing on the distance over which a force acts, we can focus on the amount of time over which a force acts.<br />We already know:<br />Ft = Δmomentum<br />And just like with kinetic energy, the momentum an object has is “set” for a given situation. <br />
  17. 17. Ft = Δmv<br />So if the Δmv is set (say from 1000 kgm/s to zero kgm/s), what happens to force as time is increased?<br />as time in increased, force is decreased<br />
  18. 18. Impulse = Change in Momentum<br />What would this relationship look like in a formula?<br />Ft = Δmv<br />The change in momentum is called impulse<br />
  19. 19. Work & Energy? Or Impulse & Momentum?<br />EITHER!<br />The work-energy theorem and the impulse-momentum theorem both describe the effect of “cushioning.”<br />As a student, it is you job to figure out which relationship is more appropriate to use given what you know about a situation.<br />
  20. 20. Designing a Safer Vehicle<br />Designing a safety device for a vehicle is often centered around finding ways to decrease the force and increase the time/distance of an impact.<br />