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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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AGENDA 17-NOV:AGENDA 17-NOV:
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
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
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.
HWHW Finish Impulse ProblemsFinish Impulse Problems Test Wednesday!Test Wednesday!
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AGENDA 24-NOV:AGENDA 24-NOV:
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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5.3 Momentum change is greater 5.3 Momentum change is greater when bouncing occurs.when bouncing occurs.
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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5.3 Momentum change is greater 5.3 Momentum change is greater when bouncing occurs.when 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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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?
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!