2. Good Morning! Today we will: conduct an investigation take some notes complete a success criteria check Please do before the bell: get your lab notebook get out something to write with get a textbook and open to page 321
4. Lab: Crumple Zones Make a new entry in your lab book. Title it, “Impulse and Changes in Momentum: Crumple Zone” Be sure to make the corresponding entry in your Table of Contents
5. Read pages 321 - 322 We will be doing Part A of the lab today. While reading about it, pay special attention to: materials you will use what you will be doing/investigating 3 minutes
6. Crumple Zones What are some of the factors that automobile designers and engineers must consider when designing a crumple zone as a safety feature? 1:2:4: Copy this question down in your lab book and jot down your ideas 2 minutes
7. Crumple Zones Share your ideas with your table partner; add anything to your list that you think of while discussing with your partner 2 min Now share with the table behind/in front of you 2 min
8. Lab: Crumple Zones 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.
9. Lab: Crumple Zones 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. 5 minutes
10. Lab: Crumple Zones 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. Diagram your design in your lab notebook. Be sure to label your design! 12 minutes
11. Lab Debrief: What works, what doesn’t? The tape doesn’t help hold the block in place when the cart crashes. Why?
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14. ΔKE = force x distance Looking at that relationship between the change in kinetic energy, force and distance, keep something in mind: 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.
15. ΔKE = force x distance So, for a given kinetic energy, what happens to force as distance is increased? as distance increases, force decreases
16. The Math of Increased Stopping Time Instead of focusing on the distance over which a force acts, we can focus on the amount of time over which a force acts. We already know: Ft = Δmomentum And just like with kinetic energy, the momentum an object has is “set” for a given situation.
17. Ft = Δmv So if the Δmv is set (say from 1000 kgm/s to zero kgm/s), what happens to force as time is increased? as time in increased, force is decreased
18. Impulse = Change in Momentum What would this relationship look like in a formula? Ft = Δmv The change in momentum is called impulse
19. Work & Energy? Or Impulse & Momentum? EITHER! The work-energy theorem and the impulse-momentum theorem both describe the effect of “cushioning.” As a student, it is you job to figure out which relationship is more appropriate to use given what you know about a situation.
20. Designing a Safer Vehicle 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.
