# 6.3 Elastic and Inelastic Collisions

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

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

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?

Conservation of Momentum
Practice Problems

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.

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

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.

Elastic Collisions

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.

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.

Elastic Collisions: Awesome Examples

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

Practice Problem

Inelastic Collisions

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.

Inelastic Collisions: Awesome Example

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

Practice Problem

Forces in Collisions

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!

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!

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.

Homework p. 230 #1-5