Momentum and Impulse

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Momentum and Impulse
HMH Physics Chapter 6 pages 190-223
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Learning Objectives

• Explain what characteristics of an object
• influence momentum and impulse.
• 2. Understand how momentum and impulse
• affect motion.
• Calculate the momentum of a physical
• system.
• 4. Calculate the impulse of a physical system.

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Momentum
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Momentum

• Momentum is a measure of how hard it is to stop
  or turn a moving object.
• What characteristics of an object would make it
  hard to stop or turn?

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• Momentum the product of an objects mass and
  velocity
• it is a vector quantity
• The direction is the same as the velocity
• The symbol is p

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Formula

• momentum mass x velocity
• p m x v
• (kgm/s) kg m/s

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• The larger the mass, the greater the momentum
  compared to a less massive object with the same
  velocity.
• If mass is constant, the larger the velocity the
  greater the momentum.
• A change in momentum over a longer time requires
  less force

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Change in momentum

• Like any change, change in momentum is calculated
  by looking at final and initial momentums.
• Dp pf pi
• Dp change in momentum
• pf final momentum
• pi initial momentum

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• Impulse the product of the force and
• the time over which it acts
  on
• an object which results in a
• momentum change of an object or
  system
• ?p
• F -------
• ?t
• unit for Impulse is Ns

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Impulse
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Impulsive Forces

• Usually high magnitude, short duration.
• Suppose the ball hits the bat at 90 mph and
  leaves the bat at 90 mph, what is the magnitude
  of the momentum change?
• What is the change in the magnitude of the
  momentum?

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Impulse (J) on a graph
F(N)
3000
2000
area under curve
1000
0
0
1
2
3
4
t (ms)
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• A change in momentum takes force and time.
• The larger the momentum, the more force and/or
  time it will take to change the momentum

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• Force and time act together to change momentum.

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• Stopping times and distance depend on the
  impulse-momentum theorem
• Impulse change in momentum
• F?t ?p
• F?t pf - pi
• F?t mvf - mvi

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• A large force over a short time will have the
  same effect as a small force over a long time.

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• A 1.7kg volleyball is served at 30m/s. How much
  momentum does the ball have?

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• The largest steam powered locomotive was built in
  the US in 1943. It is still operational and is
  used for entertainment purposes. The locomotives
  mass is 4.85 x 105kg. Suppose this locomotive is
  traveling northwest along a straight track at a
  speed of 20.0m/s. What force must the locomotive
  exert to increase its velocity to 25.0m/s to the
  northwest in 5.00s?

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• In 1991, a swedish company constructed a forklift
  truck capable of raising 9.0 x 104kg to a height
  of about 2m. Suppose a mass this size is lifted
  with an upward velocity of 12cm/s. The mass is
  initially at rest and reaches its upward speed
  because of a net force of 6.0 x 103N exerted
  upward. For how long is this force applied?

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• A 1400kg car moving westward with a velocity of
  15 m/s collides with a portapotty and is brought
  to rest in .30s. What is the force exerted on the
  car during the collision?

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• A 2250kg car traveling west slows down uniformly
  from 20.0m/s to 5.00m/s. How long does it take
  the car to slow down if the force on the car is
  8450N to the east?