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Momentum
The equation for momentum is:
Momentum is a physics term that refers to the quantity of motion that an object has. Sometimes it is defined as "inertia in motion" or "mass in motion."
The amount of momentum which an object has is dependent upon two quantities: mass (how muchstuff is moving) and velocity (how fast and in which direction the stuff is moving).
p momentum
Momentum is a vector quantity!
direction of motion
direction of momentum
direction of momentum
direction of motion
p = mv
m mass v velocity
kg
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A taxi possesses a certain amount of momentum, p. What would be the taxis's new momentum if...
a) its velocity were doubled?b) its velocity were halved?c) its mass were doubled (by adding passengers)d) both its velocity and its mass were doubled?
Sample Problem p = mv
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J = Force x Time
A force acting for a given amount of time will change the velocity of the object. If the object's velocity changes, then the object's momentum will also change.
Example
In football, the defensive player applies a force for a given amount of time to stopthe momentum of the offensive player
with the ball.
The product of force and time is referred to as impulse. It is a vector quantity. The variable for impulse is J and its units are Nm.
Δp = mΔv
Δp = m(vf vi)
J = FΔt
Change in Momentum and Impulse
Impulse(When Push Comes to Shove)
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A large impulse results if:
a) a large force acts over a short time interval.b) a small force acts over a long time interval.
J = FΔt J = FΔt
FΔt = mΔv
Impulse is equal to change in momentum.
J = Δp
FΔt = m(vf vi)
(This is equation represents Newton's second law of motion.)
Understanding Car Crashes (When Physics meets Biology)
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Momentum and Impulse
Worksheet
ANSWERS
29. a) 11.5 kgm/s east b) 2.6 x 108 kgm/s west c) 8.39 x 107 kgm/s south d) 5.88 x 1024 kgm/s north
30. 43.6 Ns down
34. 38 kgm/s away from the batter
35. 8.8 kgm/s up
37. 18 kgm/s north
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Newton's Cradle
Netwon's cradle is a device that demonstrates conservation of momentum and energy. It is constructed from a series of pendulums (usually 5) abutting one another. Each pendulum is attached to a frame by two strings of equal length angles awayed from each other. This string arrangement restricts the pendulums' movement to the same plane.
It has been a popular desk toy since being invented, named and produce in 1967 by Simon Pebble. At first a wood cradle version was sold by Harrods of London, and later a chrome design was created by sculptor Richard Loncraine.
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Sample Problems1. Two cars of equal mass are traveling down King Avenue with equal velocities. They both come to a stop over different intervals of time. The ticker tape digrams for each car are shown below.
a) At which point does each car begin to experience the impulse?
b) Which car (A or B) experiences the greatest acceleration? Justify your answer.
c) Which car experiences the greatest change in momentum? Justify your answer.
d) Which car experiences the greatest impulse? Justify your answer.
Momentum and Impulse