Transcript PPT 7 Momentum and Impulsex

Momentum Review
• What is momentum?
– “mass in motion”
• What is the equation?
• P=m*v
• What are the units?
• Kg*m/s
Momentum Review
• Is it a vector?
• Yes, because it includes
velocity
• How does the equation
work?
• If mass increases,
momentum increases. If
velocity increases, so
does momentum.
They’re directly
proportional.
Momentum Review
• If something has no motion, it has no momentum.
• Finally, if we
manipulate the mass
or velocity, what will
happen to the
momentum?
• It’ll do the same
• Can objects with
different masses and
velocities have the
same momentum?
• YES
QUICK PRACTICE
1. A 1.5 kg ball is thrown at 10 m/s. What is the
ball’s momentum?
2. A 2 kg ball has a momentum of 25 kg m/s.
What is the ball’s speed?
3. A ball is moving at 7.0 m/s and has a
momentum of 100 kg m/s. What is the ball’s
mass?
QUICK PRACTICE - ANSWERS
• 1. p = 15 kg m/s
• 2. v = 12.5 m/s
• 3. m = 14.29 kg
Momentum is hard to stop unless you have…..
Impulse
• Impulse  an action/reaction force that causes a
change in momentum
• An object with momentum can be stopped or
changed if a force is applied against it for a given
amount of time.
– the amount of time a force acts on an object is the
IMPULSE
• FORMULA  Impulse = Force * time
– Unit – N*s
Impulse-Momentum Theorem
• Impulse = Change in momentum
• In equation form, F • t = Δ mv
• If the time of impact on an object is doubled,
how is the impulse affected?
• If the time of impact on an object is extended by
4, by how much is the force of impact altered?
REAL WORLD APPLICATIONS!
BASEBALLhttp://www.youtube.com/watch?v=BQilXcnJD3o
CAR ACCIDENTS – “Crumple Zones”
https://www.youtube.com/watch?v=zS_Gk7vjmOg
“Physics of…” http://www.youtube.com/watch?v=yUpiV2I_IRI
KARATE CHOP – http://www.youtube.com/watch?v=1HNuCJ4KlYo
http://www.youtube.com/watch?v=2SkuZrU_24E
WATCH OUT FOR THAT TRAIN! http://www.youtube.com/watch?v=LCAwRnG0yho&feature=relate
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GUIDED PRACTICE
F * t = m *Δ v
F * 0.3 = 1400 * (15-0)
0.3 F = 21,000
70,000 N East
F * t = m *Δ v
3 * 1.50 = 0.5 (v)
4.5 = 0.5 v
9.00 m/s to the right
F * t = m *Δ v
Impulse = (0.40) (-22-18)
Impulse = -16 kg*m/s South
• A large milk truck with a mass of 5000 kg, is
riding at 350.0 m/s when it suddenly slams on
the brakes to avoid hitting a banana peel like
in Mario Kart. The truck loses control striking
other vehicles but eventually bring the truck
to a stop in 25 s. What average force do the
brakes exert on the truck?
F * t = m *Δ v
F (25) = (5000) (350-0)
25 F = 1,750,000
F = 70, 000 N
• If the truck had not slammed on the brakes
and had lightly pressed on them for 50
seconds. What average force would the brakes
have exerted?
F * t = m *Δ v
F (50) = (5000) (350-0)
50 F = 1,750,000
F = 35,000 N
Real – World Application?!
• Jennifer, who has a mass of 50.0 kg, is riding at
35.0 m/s in her red sports car when she must
suddenly slam on the brakes to avoid hitting a
deer crossing the road. She strikes the air bag,
that brings her body to a stop in 0.500 s. What
average force does the seat belt exert on her?
F * t = m *Δ v
F (0.5) = (50) (35-0)
0.5 F = 1750
F = 3,500 N
• If Jennifer had not been wearing her seat belt
and not had an air bag, then the windshield
would have stopped her head in 0.002 s. What
average force would the windshield have
exerted on her?
F * t = m *Δ v
F (0.002) = (50) (35-0)
0.002 F = 1750
F = 875,000 N
Exit Ticket
How would a water balloon toss be an
application of momentum and impulse?