Momentum Momentum and Collisions Momentum Banging things around…
Momentum
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Transcript of Momentum
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MomentumMomentum
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MomentumMomentum
inertia and motionNewton’s “quantity of motion”helps us understand collisions and
explosions
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Momentum and CollisionsMomentum and Collisions Elastic Collisions– objects rebound– e.g. superball
Inelastic Collisions– object stick together an usually
become distorted and generate heat– e.g. clay ball
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Momentum
Momentum = mass velocity
p = mv
Momentum is a vector quantity.
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A large truck has more momentum than a car moving at the same speed because it has a greater mass.
Which is more difficult to slow down? The car or the large truck?
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Large Momentum Examples:
– Huge ship moving at a small velocity
– High velocity bullet
P = mv
P = mv
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Impulse
In order to change the momentum of an object you must apply a force over some time interval.
Impulse = Force time interval = F t
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Impulse and Momentum
Impulse = Change in Momentum = Final (mv) - Initial (mv)
F t = (mv)
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Case 1: Increasing Momentum– Apply a force for a long time. – Examples: • Follow through on a golf swing.
– http://www.youtube.com/watch?v=Xy9GTAENiJA
• Pushing a car.
Ft
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Case 2: Decreasing Momentum – Apply a force for a long time.– Examples:• Air bags in cars.
– http://www.youtube.com/watch?v=nlWJayKWvw0– http://www.youtube.com/watch?v=_Av0WGrlTGY – http://www.youtube.com/watch?v=D-ogrMr4lWc
• Catching an egg.• Boxing, Figure 6.6• Soft collisions, Figure 6.3.
Ft
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Case 3: Decreasing Momentum– Apply a force for a short time.– Examples: • Boxing• Karate
– http://www.youtube.com/watch?v=jttqJZ9sTBk
Ft
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Conservation of MomentumThis means that the momentum doesn’t
change.
Recall that F t = mv)
In this equation, F is the "external force".
Internal forces cannot cause a change in momentum.
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ExamplesConservation of Momentum: If
there are no external forces, the total momentum for a system remains unchanged.
Example 1: a person sitting inside a car pushing against the dashboard
Example 2: a bullet fired from a rifleExample 3: a rocket is space
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Conservation of momentum
The total momentum of a group of interacting objects remains the same in the absence of external forces
Applications: Collisions, analyzing action/reaction interactions
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Question
Which has more momentum?– (A) A parked cruise ship – (B) You in your vehicle driving home
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Question
1. A force times time is most appropriately called
(a) weight(b) impulse(c) velocity(d) momentum
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Question
2. Suppose two freight cars of equal mass are coupled by a collision. This is an example of
(a) an elastic collision(b) an inelastic collision(c) none of the above
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Question
3. Which of the following is true about momentum?
(a) it is a vector(b) it is a product of mass times velocity(c) impulses are required to change it(d) all of the above