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Chapter 3, Section 7

Impulse and Changes in Momentum: Crumple Zone. Chapter 3, Section 7. Date: HW: PTG #1-8, pg. 332. Learning Objective: Explain collisions in terms of Newton’s Laws, momentum, and impulse Success Criteria: Define impulse Explain conservation of momentum. Do Now:

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Chapter 3, Section 7

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  1. Impulse and Changes in Momentum: Crumple Zone Chapter 3, Section 7

  2. Date:HW: PTG #1-8, pg. 332 • Learning Objective: • Explain collisions in terms of Newton’s Laws, momentum, and impulse • Success Criteria: • Define impulse • Explain conservation of momentum • Do Now: • Copy LO and SC on new left side page • WDYS/WDYT pg. 321 • Agenda: • Do Now • LO/SC • Physics Talk • PTG

  3. Crumple Zones! • http://www.youtube.com/watch?v=SxIDsq3wd2o • http://www.youtube.com/watch?v=e-8mlEvPzA8

  4. Physics Talk • What is a crumple zone? • Huh? • The crumple zone of an automobile is a structural feature designed to absorb energy from the impact during an accident by controlled deformation • The part of the car that “squishes” in an accident!

  5. What is the goal of a crumple zone? • Think back to dropping the eggs… • To provide a “softer” collision • The purpose of the flour (airbag) was to provide a “softer” collision

  6. Remember Work? • W=Fd=ΔKE • We decreased the force, by increasing the stopping distance, and therefore reduced the Kinetic Energy • If you increase the stopping distance, you are also increasing the amount of TIME it takes to stop!

  7. By maximizing stopping time… • …you minimize the force! • Crumple Zones increase time and decrease the force

  8. What is impulse? • A change in momentum! • Momentum can be changed by applying a FORCE during a given amount of time! • Impulse=Ft • F=Force • t=time

  9. Example: • Small force over long time produces the same impulse (Δp) as a large force over a short time. • I=20N(5s)=100kg*m/s • Crumple Zone • I=100N(1s)=100kg*m/s • OUCH!!!

  10. Why do you prefer to land on soft grass instead of hard concrete? • Less force on grass because of the increased stopping time.

  11. Work and Energy OR Impulse and Momentum? • Work-Energy increase stopping distance to decrease force • Impulse-Momentum increases stopping time to decrease force • Both are designed to protect the passenger.

  12. How does this relate to Newton’s Laws? • Newton’s 2nd Law, F=ma • If we are decreasing the force but the mass is staying the same that must mean we are also decreasing the acceleration! • Less acceleration, less force!

  13. PTG #1-8

  14. Essential Questions • Pg. 331 • What does it mean? • How do you know? • Why should you care?

  15. Exit Ticket • Explain how crumple zones help protect passengers during a collision • Use the following terms: • Force • Impulse • Momentum • Stopping distance • Stopping time

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