1 AGENDA 13-NOV: PJAS Questions? PJAS Questions? Notes – Unit 4: Momentum (chapter 5) Notes –...

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AGENDA 13-NOV:AGENDA 13-NOV:

PJAS Questions? PJAS Questions?

Notes – Unit 4: Momentum (chapter 5)Notes – Unit 4: Momentum (chapter 5)

CW – Conservation of Momentum CW – Conservation of Momentum CalculationsCalculations

HW – PJAS and finish CalculationsHW – PJAS and finish Calculations

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Chapter 5Chapter 5

MomentumMomentum

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5.1 Momentum –product of mass 5.1 Momentum –product of mass times velocitytimes velocity

Which is harder to stop when moving Which is harder to stop when moving at the same speed? 18 wheeler at the same speed? 18 wheeler truck or a sports car?truck or a sports car?

Momentum (kgMomentum (kgm/s)= Mass (kg) x velocity (m/s)m/s)= Mass (kg) x velocity (m/s)

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5.1 Momentum –product of mass 5.1 Momentum –product of mass times velocitytimes velocity

Or…Or…

p = mv p = mv

(p stands for momentum)(p stands for momentum)

Which has more momentum? A parked Which has more momentum? A parked truck or a roller skate moving at truck or a roller skate moving at 2m/s?2m/s?

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Calculating momentumCalculating momentum

1. A truck with a mass of 5000 kg is 1. A truck with a mass of 5000 kg is traveling at a rate of 50 m/s. What is traveling at a rate of 50 m/s. What is the momentum?the momentum?

p = mvp = mv

p = (5000 kg) (50 m/s)p = (5000 kg) (50 m/s)

p = 250,000 kg x m/sp = 250,000 kg x m/s

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Calculating momentumCalculating momentum

2. A car with a mass of 2500 kg is 2. A car with a mass of 2500 kg is traveling at a rate of 100 m/s. traveling at a rate of 100 m/s. Calculate momentum.Calculate momentum.

p=(2500 kg) (100 m/s)p=(2500 kg) (100 m/s)

p= 250,000 kg x m/sp= 250,000 kg x m/s

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Objective: To answer questions Objective: To answer questions and solve problems using the and solve problems using the “Law of Conservation of “Law of Conservation of Momentum”Momentum”

Notes – Impulse and Law of Notes – Impulse and Law of Conservation of MomentumConservation of Momentum

Go over homeworkGo over homework HW:HW:

p. 80 Review Questions 1- 19 Oddp. 80 Review Questions 1- 19 Odd

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5.2 Impulse changes momentum5.2 Impulse changes momentum

Momentum is Inertia in motion.Momentum is Inertia in motion.

ΔΔ p results from p results from ΔΔ in v or mass or both. in v or mass or both.

ΔΔ v means acceleration & acceleration v means acceleration & acceleration requires FORCE.requires FORCE.

Greater Force = Greater Greater Force = Greater ΔΔ p p

Time is also a factor… greater time force Time is also a factor… greater time force applied, greater applied, greater ΔΔ p! p!

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5.2 Impulse changes momentum5.2 Impulse changes momentum

Impulse = change in momentumImpulse = change in momentum(Impulse = Force x time )(Impulse = Force x time )(Momentum = Mass x velocity)(Momentum = Mass x velocity)

Therefore: Ft = Therefore: Ft = ΔΔ mv mv

To change the momentum of an To change the momentum of an object exert an impulse on itobject exert an impulse on it

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Case 1 :To increase momentumCase 1 :To increase momentum

Increase force, time (of impact) or Increase force, time (of impact) or both.both.

Ex: cannons have long barrels to Ex: cannons have long barrels to increase velocity of ball. Exploding increase velocity of ball. Exploding gunpowder gunpowder acts longeracts longer on cannonball on cannonball

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Case 2 :Decreasing momentum in Case 2 :Decreasing momentum in a long time means less force. a long time means less force.

Remember impulse = force x timeRemember impulse = force x time

A longer time decreases force.A longer time decreases force.

If you want the force of contact to be If you want the force of contact to be smaller… increase the time of smaller… increase the time of contact.contact.

EX: Crashing into a haystack or a brick EX: Crashing into a haystack or a brick wall.wall.

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Case 3 :Decreasing momentum over a Case 3 :Decreasing momentum over a SHORT TIME means SHORT TIME means MOREMORE FORCE FORCE

Don’t move “into” a punch.. Don’t move “into” a punch.. Decreased time equals more Decreased time equals more force.force.

This is the reason why we “give” This is the reason why we “give” or move away from a catch, or move away from a catch, instead of move towards it.instead of move towards it.

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5.4 Momentum is 5.4 Momentum is conservedconserved when when no external force acts on it.no external force acts on it.

Conserved Conserved – a physical quantity – a physical quantity remains unchanged. remains unchanged.

No change in momentum can occur No change in momentum can occur unless an outside force acts unless an outside force acts

EX: Pool Ball moving hits ball at rest.EX: Pool Ball moving hits ball at rest.

Total momentum conserved.Total momentum conserved.

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Law Of Conservation of MomentumLaw Of Conservation of Momentum

In the absence of an external force, In the absence of an external force, the momentum of a the momentum of a systemsystem remains remains unchanged.unchanged.

(net momentum before & after event (net momentum before & after event is the same)is the same)

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AGENDA 18-NOV:AGENDA 18-NOV: Objective: To describe the Objective: To describe the

difference between elastic and difference between elastic and inelastic collisions.inelastic collisions.

Go to:Go to: http://moourl.com/collision http://moourl.com/collision

Describe the difference between Describe the difference between the two types of collisionsthe two types of collisions

Notes – Elastic & Inelastic Notes – Elastic & Inelastic CollisionsCollisions

HW: Collision Practice ProblemsHW: Collision Practice Problems

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5.5 Momentum is conserved in 5.5 Momentum is conserved in collisionscollisions

Net momentum before collision = Net Net momentum before collision = Net momentum after collision.momentum after collision.

Internal forces only Internal forces only

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Elastic CollisionsElastic Collisions when objects collide w/o lasting when objects collide w/o lasting

deformation or heat generation. deformation or heat generation. Colliding objects bounce perfectlyColliding objects bounce perfectly Ex: Ex: billiard ballsbilliard balls

Book Ex:Book Ex:P. 77 figure 5.12P. 77 figure 5.12

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Ex Problem Ex Problem

Ball a has a mass of 1kg and is moving Ball a has a mass of 1kg and is moving with a velocity of 5 m/s collides with a velocity of 5 m/s collides elastically with ball b Which has a mass elastically with ball b Which has a mass of 2 kg and is at rest (0 m/s). What is of 2 kg and is at rest (0 m/s). What is the velocity of ball 2 after the collision? the velocity of ball 2 after the collision? Ball A is now at rest.Ball A is now at rest.

Let’s Review HW problems #6, 7, 9Let’s Review HW problems #6, 7, 9

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Inelastic Collisions- Inelastic Collisions- When objects collide & become When objects collide & become

entangled. They become deformed, entangled. They become deformed, or heat is generated.or heat is generated.

Objects stick together and move as Objects stick together and move as oneone

Book EX: P. 77 figure 5.13 & 5.14Book EX: P. 77 figure 5.13 & 5.14

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Formula for inelastic collisionsFormula for inelastic collisions

[Ma Va + Mb Vb] before = [ (Ma + Mb) v] [Ma Va + Mb Vb] before = [ (Ma + Mb) v] afterafter

Lets review some problems…. #8 & 10.Lets review some problems…. #8 & 10.

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Start Collision Practice Start Collision Practice Problem PacketProblem Packet

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P. 80-82P. 80-82

Do review questions # 2-10 EvenDo review questions # 2-10 Even

Exercises: # 2 – 8 evenExercises: # 2 – 8 even

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Submit Collisions WSSubmit Collisions WS

Momentum LabMomentum Lab

HW – Lab Write Up, PJAS #5 Due, HW – Lab Write Up, PJAS #5 Due, Test Wednesday 11/26Test Wednesday 11/26

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Submit Lab Write UpSubmit Lab Write Up

Momentum Quiz!Momentum Quiz!

CW – Impulse ProblemsCW – Impulse Problems

HWHW Finish Impulse ProblemsFinish Impulse Problems Test Wednesday!Test Wednesday!

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Review & Submit HWReview & Submit HW

Last Day of Notes! Last Day of Notes!

CW – Trends in Momentum WS, CW – Trends in Momentum WS, Momentum and Impulse ReviewMomentum and Impulse Review

HWHWWORK ON PacketWORK ON PacketTest Wednesday!Test Wednesday!PJAS RESULTS DUE FRIDAY!PJAS RESULTS DUE FRIDAY!

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5.3 Momentum change is greater 5.3 Momentum change is greater when bouncing occurs.when bouncing occurs.

Remember:Remember: an unbalanced force an unbalanced force

always accelerates an always accelerates an object - either speeding object - either speeding it up or slowing it downit up or slowing it down

Impulse = Change in Impulse = Change in momentummomentum

F x t = F x t = ΔΔ m x v m x v

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the impulse experienced by an the impulse experienced by an object is the force*time object is the force*time

the momentum change of an object the momentum change of an object is the mass*velocity change is the mass*velocity change

the impulse equals the momentum the impulse equals the momentum change change

Why does it require a greater Why does it require a greater impulse to bring an object to a stop impulse to bring an object to a stop & “throw it back again”?& “throw it back again”?

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““Rebounding” requires a greater Rebounding” requires a greater impulse because it results in a impulse because it results in a greater change in velocity!greater change in velocity!

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P.80-81 P.80-81

Review questionsReview questions

#11,12,14,18,19,20#11,12,14,18,19,20

Are you ready to take the test?Are you ready to take the test?

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HW checkHW check

CW – Study GuideCW – Study Guide

HWHWSTUDYSTUDYTest Tomorrow!Test Tomorrow!

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AGENDA (?+1)-JAN:AGENDA (?+1)-JAN:

Review MomentumReview Momentum

CW – Start Review PacketCW – Start Review Packet

HWHWBINDER CHECK TOMORROWBINDER CHECK TOMORROWSTUDYSTUDYQPA TomorrowQPA Tomorrow

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Calculating MomentumCalculating Momentum

Momentum = mass x velocityMomentum = mass x velocity

p = mv p = mv

An object MUST have velocity in order An object MUST have velocity in order to have momentum!to have momentum!

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Momentum is conserved in Momentum is conserved in collisionscollisions

Net momentum before collision = Net Net momentum before collision = Net momentum after collision.momentum after collision.

Elastic collision – PERFECTElastic collision – PERFECT– m1v1 (before) = m2v2 (after) m1v1 (before) = m2v2 (after)

Inelastic collision – objects stick Inelastic collision – objects stick together post collisiontogether post collision– m1v1 + m2v2 = (m1+m2)vm1v1 + m2v2 = (m1+m2)v

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Impulse changes momentumImpulse changes momentum

Impulse = change in momentumImpulse = change in momentum(Impulse = Force x time )(Impulse = Force x time )(Momentum = Mass x velocity)(Momentum = Mass x velocity)

Therefore: Ft = Therefore: Ft = ΔΔ mv mv

To change the momentum of an To change the momentum of an object exert an impulse on itobject exert an impulse on it

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Decreasing momentum in a long Decreasing momentum in a long time means less force. time means less force.

Remember impulse = force x timeRemember impulse = force x time

A longer time decreases force.A longer time decreases force.

If you want the force of contact to be If you want the force of contact to be smaller… increase the time of smaller… increase the time of contact.contact.

EX: Crashing into a haystack or a brick EX: Crashing into a haystack or a brick wall. Crash into the haystack!wall. Crash into the haystack!

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Momentum change is greater when Momentum change is greater when bouncing occurs.bouncing occurs.

““Rebounding” requires a greater Rebounding” requires a greater impulse because it results in a impulse because it results in a greater change in velocity!greater change in velocity!

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