Download Lesson 02 - MnE - Change in Momentum

Momentum and Momentum
Changes
Lesson 2
Thursday, October 13, 2011
Announcements
HW #1 due today
 HW #2 due tomorrow
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Physics “Lunch Bunch” will meet this
week (Lens Lab)
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Optics exam Friday
AP Physics B Standards
Momentum and Momentum Change
LESSON 2:
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I.D.2. Impulse and Momentum
Students should understand impulse and linear
momentum, so they can:
a) Relate mass, velocity, and linear momentum for a moving object
b) Relate impulse to the change in linear momentum and the
average force acting on an object.
d) Calculate the area under a force versus time graph and relate it
to the change in momentum of an object.
Lesson Objectives
Students will be able to
1. Calculate the momentum of an object.
2. Apply the impulse momentum theorem to
various systems.
Which do you think has more
momentum?
Momentum
Momentum is a measure of how hard it is to stop or turn
a moving object.
Q: What characteristics of an object would make it hard
to stop or turn?

Let’s watch Mad Scientist Guy on Momentum and
Newton’s Third Law of Motion!
Calculating Momentum
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For one particle
p = mv
Note that momentum is a vector with the same
direction as the velocity!
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For a system of multiple particles
p = pi --- add up the vectors
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The unit of momentum is…
kg m/s or Ns
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Sample Problem 2.1:
Calculate the momentum of a system composed of a 65-kg sprinter running
east at 10 m/s and a 75-kg sprinter running north at 9.5 m/s.
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Sample Problem 2.1:
Calculate the momentum of a system composed of a 65-kg sprinter running
east at 10 m/s and a 75-kg sprinter running north at 9.5 m/s.
Impulse-momentum theorem
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An impulse exerted on a system will
change the momentum of a system.
J = p
FΔt = pf – pi
Momentum change
demonstration
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Using only a meter stick, find the momentum
change of each ball when it strikes the desk from a
height of exactly one meter.
Which ball, Bouncy or Lazy, has the greatest
change in momentum?
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Sample Problem 2.2:
Use the impulse-momentum theorem to find out how long a stone falling
straight down takes to increase its speed from 5.5 m/s to 10.4 m/s.
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Sample Problem 2.3:
A 2.0 kg object is moving to the right with a speed of 1.0 m/s when it
experiences the force shown below.
What are the object’s speed and direction after the force ends?