1 PHY 113 C General Physics I 11 AM 1215 P M MWF Olin 101 Plan for Lecture 10 Chapter 9 Linear momentum Impulse and momentum Conservation of linear momentum Examples collision ID: 639168
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10/01/2013
PHY 113 C Fall 2013 -- Lecture 10
1
PHY 113 C General Physics I
11 AM – 12:15
P
M MWF Olin 101
Plan for Lecture 10
Chapter
9 -- Linear momentum
Impulse and momentum
Conservation of linear momentum
Examples – collision
analysis
Notion of center of massSlide2
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Summary of physics “laws”Slide4
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Another way to look at Newton’s second law:
iclicker
question:
Why would you want to define linear momentum?
To impress your friends.
To exercise your brain.
It might be helpful.
To distinguish it from angular momentum.Slide5
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Relationship between Newton’s second law and linear momentum:
(if
m
is constant)Slide6
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Suppose that a tennis ball with mass m=0.057 kg approaches a tennis racket at a speed of 45m/s. What is the impulse the racket must exert on the ball to return the ball in the opposite direction at the same speed. Assume that the motion is completely horizontal.Slide8
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Example: A 1500 kg car collides with a wall, with
v
i
= -15m/s and
v
f
=2.6m/s. What is the impulse exerted on the car?Slide9
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Example of graphical representation of F(t)Slide10
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Physics of composite systemsSlide11
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Example – completely
inelastic
collision; balls moving on a frictionless surfaceSlide12
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Energy loss in this example:Slide13
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Example – completely
elastic
collision; balls moving on a frictionless surfaceSlide14
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Completely elastic collision; numerical example:Slide15
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iclicker
exercise:
We have assumed that there is no net force acting on the system. What happens if there are interaction forces between the particles?
Analysis still applies
Analysis must be modifiedSlide16
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Example from homework:Slide17
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Example from homework
: -- continued
iclicker
question
Do you expect
K
f
-K
i
to be
>0
<0Slide18
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Another example:
before
v
f
afterSlide19
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Examples of two-dimensional collision;
balls
moving on a frictionless surfaceSlide20
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Examples of two-dimensional collision;
balls
moving on a frictionless surfaceSlide21
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Example: two-dimensional totally inelastic collision
m
1
=1500kg
m
2
=2500kgSlide22
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iclicker
exercise:
Can this analysis be used to analyze a real collision?
Of course! The laws of physics must be obeyed.
Of course NOT! In physics class we only deal with idealized situations which never happen.Slide23
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Another example of 2-dimensional elastic collision:
m
v
i
v
f
mSlide24
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Energy analysis of a simple nuclear reaction :
Q=4.87 MeVSlide25
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Energy analysis of a simple reaction :
Q=4.87 MeVSlide26
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Elastic collision in two dimensionsSlide27
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Elastic collision in two dimensions --
example of elastic proton-proton scatteringSlide28
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Elastic collision in two dimensions --
example of elastic proton-proton scatteringSlide29
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The notion of the center of mass and the physics of composite systemsSlide30
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Finding the center of massSlide32
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Example from
webassign
:
x
y
m
1
m
2
m
3
m
4Slide33
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Finding the center of mass
For a solid object composed of constant density material, the center of mass is located at the center of the object.