Ch 6 3 Elastic and Inelastic Collisions Bell

Ch. 6. 3 Elastic and Inelastic Collisions

Bell Ringer n A 40 kg miniature horse runs west at 8 m/s. What is the force of impact if it hits a wall and comes to a stop in 0. 5 s?

Objectives We will demonstrate and apply the laws of conservation of momentum in one dimension. n n n I will complete a worksheet, notetaking & drawing to demonstrate & apply conservation of momentum in elastic & inelastic collisions (6 D)

AGENDA n n n conservation of momentum Intro to types of collisions&Examples inelastic vs elastic collisions Complete worksheet Reminder: Egg drop- next Tuesday 1/17 Missed Friday assignment- Thursday is last day!

Conservation of Momentum n Principle that states that the total momentum of an isolated system stays constant. ¡ Total momentum before a collision equals total momentum after a collision p = 30 kg·m/s p = 20 kg·m/s Total = 50 kg·m/s p = 20 kg·m/s p = 30 kg·m/s Total = 50 kg·m/s

Conservation of Momentum Equation n

Demo: Newton’s Cradle

Newton’s Cradle

Demo: Basketball and Tennis Ball

Conservation of Momentum in Two Dimensions

Conservation of Momentum in Two Dimensions Before After

Examples n

Collisions How would you define “collision? ” ●Is a tennis racket hitting a ball a collision? ●Is a baseball glove catching a baseball a collision? ●What’s different about these two situations? ●

Collisions [NBC Learn Video-NHL] Collisions happen whenever two objects impact each other ● Sometimes the objects bounce off of each other Sometimes the objects stick together

Types of Collisions n Elastic n Inelastic n Perfectly inelastic

Elastic vs Inelastic Collisions Elastic Perfectly Inelastic

Perfectly Inelastic Collisions In a perfectly inelastic collision, two objects collide and stick to each other with some deformation ● deformation m 1 v 1 + m 2 v 2 = (m 1 + m 2)v’ Kinetic energy is NOT conserved because deformation takes away energy (sound, friction, etc. ) ●Momentum is conserved: p = p i f ●

Examples of Perfectly Inelastic Collisions

Elastic Collisions In an elastic collision, two objects collide and bounce off of each other ● m 1 v 1 + m 2 v 2 = m 1 v’ 1 + m 2 v’ 2 Kinetic energy is conserved because motion continues uninterrupted: KEi = KEf ●Momentum is conserved: p = p i f ●

Real World Examples

Typical Elastic Collisions

Realistic Collisions some deformation Most collisions are somewhere between elastic and perfectly inelastic ●For our class, we will be assuming collisions are either elastic or perfectly inelastic ●

Real World Examples

Problem Set ●Rd the problem. ●Sketch a before & after pic to determine whether it is an elastic or inelastic collision ●Choose the appropriate formula ●Identify variables: m 1, v 1, m 2, v’ 1 etc. ●Solve