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Chapter 3 Section 3. Energy and Work: Why Air Bags?. Physics 3.3: Energy and Work Homework 1-10, Skip 4 and 7 Due Friday. Learning Objective Students will be able to describe the relationship between stopping distance and force required to stop an object Success Criteria

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Chapter 3 Section 3

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Chapter 3 Section 3

Energy and Work: Why Air Bags?


Physics 3.3: Energy and WorkHomework 1-10, Skip 4 and 7 Due Friday

  • Learning Objective

    • Students will be able to describe the relationship between stopping distance and force required to stop an object

  • Success Criteria

    • Model an automobile air bag

    • Relate W=F·D to the eggsperiment (get it?)

  • Do Now:

    • QUIZ!

  • Agenda

    • Do Now

    • Investigate 3.3

    • Summary/Exit Ticket


Egg Lab 

  • Dropping Eggs!

  • Throwing an egg in a blanket


Exit Ticket

  • How did the indentation of the egg in the flour change as you increased the initial drop height?


Physics Talk 3.3

  • Learning Objective

    • Students will be able to explain the relationship between work and kinetic energy

  • Success Criteria

    • Students will be able to explain the relationship between stopping distance and force required to stop

    • Students will be able to explain the relationship between velocity and braking distance

    • Students will describe which features of a car help in the case of a collision

  • Do Now:

    • WDYS/WDYT p 277

  • Agenda

    • Do Now

    • Physics Talk 3.3

    • What do you think now?

    • Summary


Physics Talk 3.3

  • What is kinetic energy?

  • What is the equation?

  • The energy an object has because of its motion.


Kinetic Energy and the Eggs

  • The two eggs were dropped from the same height. Which had more kinetic energy?

  • Since both eggs had approximately the same mass and same relative velocity, they about the same kinetic energy.


Measuring Force Over a Distance

  • How was the egg able to stop?

  • How do you measure the distance in each egg drop?

  • The surface had to apply a force over some distance.

  • When the egg was dropped in flour, you can measure the indentation. With the hard surface, you cannot see the indentation.


Braking a Car

  • How do auto brakes work?

  • The braking system has to eliminate the kinetic energy of the vehicle by applying a large force over a large distance.


Work

  • How do you calculate work?

  • How does work relate to kinetic energy?

  • W=F·D

  • Work is the change in kinetic energy. We can write this as


Braking a Car


Example


What about the eggs?

  • How does this apply to the eggs?

  • When the egg could be stopped over a greater distance, there was less damage to it because less force had to be applied.


  • How does this apply to a car crash?

  • Airbags! These allow you to have more distance to stop your body so you will be less likely to get hurt.


  • If you are traveling three-times the speed, will you need three times the braking distance?

  • False! You will need 9 times the stopping distance. This is because in the formula, the velocity is squared


  • Why is it harder to stop on icy or wet roads?

  • The slippery surface makes it more difficult to supply a sufficient force, so it is necessary to give yourself more distance.


  • What else helps stop an automobile?

  • The crumple zone of a car allows the car to have more distance to stop. This is why cars are designed to dent and are not made out of more sturdy material.


Sample Problem

  • p286 and 287 Sample Problem


What do you think now?

Exit Ticket: How does and air bag protect you during an accident?


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