2 Agenda Today: Friday: Monday: Tomorrow Tuesday Thursday: Finish Collisions (7.3)Warm UpFriday:Review HW from 7.1Problem Solving PracticePractice Problems for 7.2Monday:Intro to Collisions (7.3)TomorrowConcepts ReviewTuesdayConservation of Momentum LabChapter 6 TestThursday: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?
5 Practice ProblemsRecoil: 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 #39As 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 CollisionsForces 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.
9 Collisions Collisions can be categorized into two types: elasticinelasticElastic 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 otherNo 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.
15 Inelastic Collisions In inelastic collisions objects: Stay stuck togetherKinetic energy is lost to:Primarily internal energyHeatSoundObjects 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.
20 Forces in CollisionsAssume 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.
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