Lecture series for Conceptual Physics 8th Ed'

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Lecture series for Conceptual Physics 8th Ed.
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Rotational Inertia p118
Alias momentum of inertia.
The property of an object to resist being rotated
T.R. Walker starts to fall.
So, he pushes down on his right and pulls up on
his left to right himself. The pole stays put.
Whose legs have the least rotational inertia in
fig. 7.3?
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Fig 7.5 Rotational inertias of some shapes
Why does disk beat hoop down ramp?
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Torque p121
Torque lever arm x force
fulcrum
force
mg
At equilibrium CCW torque CW torque
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Fl x dl Fr x dr 300 x dl500 x 1.5
dl2.5m
Torque la x F F x d
Huh?
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Center of Mass and Center of Gravity p123
Fig 7.11 shows the ball following a smooth
parabola and the bat wobbling.
In both cases, the CM makes a smooth parabola.
The white dot marks the CM of the adjustable
wrench.
The CM goes straight!
Center of Gravity is basically the same as CM.
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Locating the Center of Gravity p 124
Tccw Tcw
NOTE The weight of the stick acts at its center
of gravity.
For weird shapes
For athletes
Which one is more stable?
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Stability p125
Equilibrium exist when your CG is over your
support.
Whoops!
The amount of stability is determined by how high
the CG must be raised in order to tip the object
over.
Most stable
Umgh?
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More Stability
In fig. 7.24 which has the greater torque around
the imaginary fulcrum?
No
This one?
What contributes to its greater torque?
Yes
This one?
Longer lever arm
More mass (force).
Peter Parker fooling around.
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Centripetal Force p128
The force on a moving object that is directed
towards a fixed center.
Is the water forced away from the clothes?
No!
The clothes are forced away from the water.
5g 1g
Loose mud flies off on a tangent.
5g 1g
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Centrifugal (the imaginary) force p129
When the car stops and youre thrown against
the dashboard, you dont say a force pushed you
forward.
You say, My inertia kept me going and the
dashboard pushed on me.
The bug wants to go in a straight line but the
can pushes it toward the center
Does the bug say, Im pushing on the floor?
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Centrifugal Force in a Rotating Frame p130
The silly bug still thinks that it is in a
stationary can pushing on the floor.
You are lighter at the equator.
Bugs in the space tire think that they have
gravity.
?
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Simulated Gravity p 131
A force toward the center.
The reaction force
The action force
But, this is an imaginary force.
If the floor were to give way, would he fly away
from the center?
NO!
He would sail off on the tangent.
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Angular Momentum p133
You remember, of course, that linear momentum,
p, m x v.
Since mass and inertia are aspects of the same
thing, then you wouldnt be surprised that
AnguLar momentum rotational inertia x
rotational velocity
L I
(I mr2 or I ½ mr2, etc.)
Given
v
v / r
So, L mr2
mvr
r
What is angular momentum of the ball if m 2kg,
v 3m/s and r 4m?
Lmvr(2)(3)(4) 24kg-m2/s
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Conservation of Angular Momentum p134
I
A falling cat rotates its front half to rotate
the back in the other direction, then straightens
out for a 4 footed landing

I
A gymnast balls up to increase his spin rate.
The end