02-18-09 notes: momentum
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TRANSCRIPT
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Notes: Momemtum
CW: Acceleration and Momentum
H: The Laws of Motion
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Momentum
2-18-09
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Objectives
1. describe the relationship between mass, velocity, inertia, and momentum
2. relate conservation of momentum to motion in a collision
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What makes an object difficult to stop?
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Calculating MomentumThe momentum of an object is
directly related to its mass and its velocity.
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MassMass measures inertia. The mass of an object tells you how much the object resists accelerating.
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Nothing will change speed unless acted upon by a force. If it’s sitting still, it will keep sitting still. If it’s moving fast, it will keep moving fast.
Only a force can change the velocity of an object.
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Velocity
Fast objects are also difficult to stop.
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Momentum = (mass)(velocity)
p = mv
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Example
A ball of mass 2 kg is moving with a speed of 4 m/s.
What is its momentum?
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SolutionMomentum = (mass)(velocity)
p = mv
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p = (2 kg)(4 m/s)
p = 8 kg m/s
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ExampleA runner has a mass of 75 kg and is running at 6 m/s.
What is his momentum?
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SolutionMomentum = (mass)(velocity)
p = mv
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p = (75 kg)(6 m/s)
p= 450 kg m/s
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Momentum is a vector quantity. Its direction is the same as the direction of the object's velocity.
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Elastic collision
Resulting momentum
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Two dimensional collision
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Knowing the momentum of moving objects helps explain what happens when objects collide with one another.
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Although moving objects can collide in many different ways, they have one important thing in common.
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Law of Conservation of Momentum
The total momentum before and after the collision is not changed by the collision.
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