1 AGENDA 13-NOV: PJAS Questions? PJAS Questions? Notes – Unit 4: Momentum (chapter 5) Notes – Unit 4: Momentum (chapter 5) CW – Conservation of Momentum Calculations CW – Conservation of Momentum Calculations HW – PJAS and finish Calculations HW – PJAS and finish Calculations

2 Chapter 5 Momentum

3 5.1 Momentum –product of mass times velocity Which is harder to stop when moving at the same speed? 18 wheeler truck or a sports car? Momentum (kg  m/s)= Mass (kg) x velocity (m/s)

4 5.1 Momentum –product of mass times velocity Or… p = mv (p stands for momentum) Which has more momentum? A parked truck or a roller skate moving at 2m/s?

5 Calculating momentum 1. A truck with a mass of 5000 kg is traveling at a rate of 50 m/s. What is the momentum? p = mv p = mv p = (5000 kg) (50 m/s) p = 250,000 kg x m/s

6 Calculating momentum 2. A car with a mass of 2500 kg is traveling at a rate of 100 m/s. Calculate momentum. p=(2500 kg) (100 m/s) p=(2500 kg) (100 m/s) p= 250,000 kg x m/s p= 250,000 kg x m/s

7 AGENDA 17-NOV: Objective: To answer questions and solve problems using the “Law of Conservation of Momentum” Objective: To answer questions and solve problems using the “Law of Conservation of Momentum” Notes – Impulse and Law of Conservation of Momentum Notes – Impulse and Law of Conservation of Momentum Go over homework Go over homework HW: HW: p. 80 Review Questions Odd p. 80 Review Questions Odd

8 5.2 Impulse changes momentum Momentum is Inertia in motion. Δ p results from Δ in v or mass or both. Δ v means acceleration & acceleration requires FORCE. Greater Force = Greater Δ p Time is also a factor… greater time force applied, greater Δ p!

9 5.2 Impulse changes momentum Impulse = change in momentum (Impulse = Force x time ) (Momentum = Mass x velocity) Therefore: Ft = Δ mv To change the momentum of an object exert an impulse on it

10 Case 1 :To increase momentum Increase force, time (of impact) or both. Ex: cannons have long barrels to increase velocity of ball. Exploding gunpowder acts longer on cannonball

11 Case 2 :Decreasing momentum in a long time means less force.  Remember impulse = force x time A longer time decreases force. If you want the force of contact to be smaller… increase the time of contact. EX: Crashing into a haystack or a brick wall.

12 Case 3 :Decreasing momentum over a SHORT TIME means MORE FORCE  Don’t move “into” a punch.. Decreased time equals more force. This is the reason why we “give” or move away from a catch, instead of move towards it.

Momentum is conserved when no external force acts on it.  Conserved – a physical quantity remains unchanged.  No change in momentum can occur unless an outside force acts EX: Pool Ball moving hits ball at rest. Total momentum conserved.

14 Law Of Conservation of Momentum In the absence of an external force, the momentum of a system remains unchanged. (net momentum before & after event is the same)

15 AGENDA 18-NOV: Objective: To describe the difference between elastic and inelastic collisions. Objective: To describe the difference between elastic and inelastic collisions. Go to: Go to: Describe the difference between the two types of collisions Describe the difference between the two types of collisions Notes – Elastic & Inelastic Collisions Notes – Elastic & Inelastic Collisions HW: Collision Practice Problems HW: Collision Practice Problems

Momentum is conserved in collisions Net momentum before collision = Net momentum after collision.  Internal forces only

17 Elastic Collisions  when objects collide w/o lasting deformation or heat generation.  Colliding objects bounce perfectly  Ex: billiard balls billiard balls Book Ex: P. 77 figure 5.12

18 Ex Problem Ball a has a mass of 1kg and is moving with a velocity of 5 m/s collides elastically with ball b Which has a mass of 2 kg and is at rest (0 m/s). What is the velocity of ball 2 after the collision? Ball A is now at rest. Let’s Review HW problems #6, 7, 9

19 Inelastic Collisions- When objects collide & become entangled. They become deformed, or heat is generated.  Objects stick together and move as one  Book EX: P. 77 figure 5.13 & 5.14

20 Formula for inelastic collisions [Ma Va + Mb Vb] before = [ (Ma + Mb) v] after Lets review some problems…. #8 & 10.

21 Start Collision Practice Problem Packet

22 P Do review questions # 2-10 Even Exercises: # 2 – 8 even

23 AGENDA 20-NOV: Submit Collisions WS Submit Collisions WS Momentum Lab Momentum Lab HW – Lab Write Up, PJAS #5 Due, Test Wednesday 11/26 HW – Lab Write Up, PJAS #5 Due, Test Wednesday 11/26

24 AGENDA 21-NOV: Submit Lab Write Up Submit Lab Write Up Momentum Quiz! Momentum Quiz! CW – Impulse Problems CW – Impulse Problems HW HW Finish Impulse Problems Finish Impulse Problems Test Wednesday! Test Wednesday!

25 AGENDA 24-NOV: Review & Submit HW Review & Submit HW Last Day of Notes! Last Day of Notes! CW – Trends in Momentum WS, Momentum and Impulse Review CW – Trends in Momentum WS, Momentum and Impulse Review HW HW WORK ON Packet WORK ON Packet Test Wednesday! Test Wednesday! PJAS RESULTS DUE FRIDAY! PJAS RESULTS DUE FRIDAY!

Momentum change is greater when bouncing occurs. Remember:  an unbalanced force always accelerates an object - either speeding it up or slowing it down  Impulse = Change in momentum  F x t = Δ m x v

Momentum change is greater when bouncing occurs.  the impulse experienced by an object is the force*time  the momentum change of an object is the mass*velocity change  the impulse equals the momentum change  Why does it require a greater impulse to bring an object to a stop & “throw it back again”?

Momentum change is greater when bouncing occurs.  “Rebounding” requires a greater impulse because it results in a greater change in velocity!

29 P Review questions #11,12,14,18,19,20  Are you ready to take the test?

30 AGENDA 25-NOV: HW check HW check CW – Study Guide CW – Study Guide HW HW STUDY STUDY Test Tomorrow! Test Tomorrow!

31 AGENDA (?+1)-JAN: Review Momentum Review Momentum CW – Start Review Packet CW – Start Review Packet HW HW BINDER CHECK TOMORROW BINDER CHECK TOMORROW STUDY STUDY QPA Tomorrow QPA Tomorrow

32 Calculating Momentum Momentum = mass x velocity p = mv An object MUST have velocity in order to have momentum!

33 Momentum is conserved in collisions  Net momentum before collision = Net momentum after collision.  Elastic collision – PERFECT –m1v1 (before) = m2v2 (after)  Inelastic collision – objects stick together post collision –m1v1 + m2v2 = (m1+m2)v

34 Impulse changes momentum Impulse = change in momentum (Impulse = Force x time ) (Momentum = Mass x velocity) Therefore: Ft = Δ mv To change the momentum of an object exert an impulse on it

35 Decreasing momentum in a long time means less force.  Remember impulse = force x time A longer time decreases force. If you want the force of contact to be smaller… increase the time of contact. EX: Crashing into a haystack or a brick wall. Crash into the haystack!

36 Momentum change is greater when bouncing occurs.  “Rebounding” requires a greater impulse because it results in a greater change in velocity!