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March 24, 2006
1
Engineers 1
Engineers 1
Spring Semester 2006
Lecture 36
March 24, 2006
2
Review: Torque
Review: Torque
r
!
=
r
r
"
r
F
March 24, 2006
3
Review: Angular Momentum
Review: Angular Momentum
!
The angular momentum of a point particle
!
The magnitude of the angular
momentum
!
Angular momentum and torque:
!
For rigid objects (and only for
them):
r
L
=
r
r
!
r
p
L
=
rp
sin
d
dt
r
L
=
r
r
L
=
I
r
March 24, 2006
4
Torque and Angular Acceleration
Torque and Angular Acceleration
!
Starting with our expression for the angular
momentum of a rigid body we can show
(I of a rigid body is constant)
!
We can see the analogy of this result
!
with Newton’s Second Law
d
dt
r
L
=
d
dt
(
I
r
)
=
I
d
dt
r
=
I
r
"
=
r
#
r
=
I
r
r
F
=
m
r
a
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View Full DocumentMarch 24, 2006
5
Quiz 34.1
Quiz 34.1
!
A mass is twirled by a thread in a vertical
circle of
constant radius. At what part of the circle does
the mass have a nonzero (instantaneous) angular
acceleration?
A) At the top
B) At the bottom
C) At midheight
D) The angular acceleration
is zero at all points on the
circle.
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 Spring '08
 Wolf
 Physics, Angular Momentum, Momentum

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