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

Date: HW: PTG #1-8, pg. 332 Learning Objective: Success Criteria: 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

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

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!

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

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!

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

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

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!!!

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

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.

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!

PTG #1-8

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

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