1. 6.3 Elastic and Inelastic Collisions
Date, Section, Pages, etc.
Mr. Richter

2. Agenda Today: Friday: Monday: Tomorrow Tuesday Thursday:
Finish Collisions (7.3)
Warm Up
Friday:
Review HW from 7.1
Problem Solving Practice
Practice Problems for 7.2
Monday:
Intro to Collisions (7.3)
Tomorrow
Concepts Review
Tuesday
Conservation of Momentum Lab
Chapter 6 Test
Thursday:
Review HW from 7.2

3. Warm-Up:
Assume two cars have the same mass and speed going into a collision.
Scenario A: Two cars collide with each other but bounce off. Neither of them sustain noticeable damage.
Scenario B: Two cars collide with each other and crumple, sticking together after the crash.
In which scenario do you think energy is conserved?
In which scenario do you think the driver feels more force?

4. Conservation of Momentum
Practice Problems

5. Practice Problems
Recoil: A boy on a skateboard initially at rest tosses an 8.0 kg jug of water in the forward direction at a speed of 3.0 m/s. If the boy and the skateboard move backward at m/s, find the mass of the boy.
Collision: p. 234 #39
As long as everything is in grams (g) and centimeters per second (cm/s), THERE IS NO NEED TO CONVERT.

6. Agenda Review HW from 6.2 Recap Elastic and Inelastic Collisions
Problem Solving with Elastic and Inelastic Collisions
Forces in Elastic and Inelastic Collisions

7. Objectives Identify different types of collisions.
Calculate change in kinetic energy (or lack thereof) in different types of collisions.
Find the final velocity of objects in different types of collisions.
Understand the relationship between the type of collision and the force experienced by the object.

8. Elastic Collisions

9. Collisions Collisions can be categorized into two types:
elastic
inelastic
Elastic collisions are when objects bounce off of each other.
(Elastics are like rubber bands, and rubber bounces)
Scenario A.
Inelastic collisions are when objects stick together after the crash.
Scenario B.

10. Elastic Collisions In perfectly elastic collisions objects:
Bounce off each other
No loss of energy due to speed (kinetic energy)
No change of shape.
In real life, there are almost no perfectly elastic collisions.
Almost always, some energy is lost to sound or heat in a collision.

11. Elastic Collisions: Awesome Examples

12. Elastic Collisions: Problem Solving
Both momentum and kinetic energy are conserved in perfectly elastic collisions. Masses separate afterward.

13. Practice Problem

14. Inelastic Collisions

15. Inelastic Collisions In inelastic collisions objects:
Stay stuck together
Kinetic energy is lost to:
Primarily internal energy
Heat
Sound
Objects are deformed (shape is changed.
In real life, most collisions are a combination of elastic and inelastic collisions. Objects will deform a little, and separate a little.

16. Inelastic Collisions: Awesome Example

17. Inelastic Collisions: Problem Solving
Only momentum is conserved in inelastic collisions. Kinetic energy is lost. Masses stick together afterward.

18. Practice Problem

19. Forces in Collisions

20. Forces in Collisions
Assume two objects that have the same mass and the same speed collide with each other.
In which type of collision do they experience a greater change in momentum?
inelastic (both vehicles stop)
elastic (both vehicles stop and reverse direction)
Elastic collisions have greater changes in speed, thus the objects experience more force!

21. Forces in Collisions: Examples
Think of a batter in baseball. Does the baseball experience more force when the batter:
bunts (inelastic)
hits a home run (elastic)
Your car is designed to crumple (inelastic), so that you experience less force.
Greater changes in momentum mean more force. Elastic collisions are more forceful!

22. Wrap-Up: Did we meet our objectives?
Identify different types of collisions.
Calculate change in kinetic energy (or lack thereof) in different types of collisions.
Find the final velocity of objects in different types of collisions.
Understand the relationship between the type of collision and the force experienced by the object.

23. Homework
p. 230 #1-5