Angular Momentum
Friday, November 7
Exam 3 Average = 83
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Today: Angular Momentum
Chapter 9 Section 7
Angular Momentum, L
L  I
Direction??
Compare to linear momentum
p  mv
Conservation of Angular Momentum
Li  L f
I ii  I f  f
What is needed for L to be conserved?
Problem 9.34
Divers change their body position in midair while
rotation about their c of m. A diver leaves the board
with her body nearly straight, then tucks into a
somersault position. If her moment of inertia in the
straight position is 14 kg•m2 and in tuck is 4.0 kg•m2
by what factor is her angular velocity when tucked
greater than when straight?
Problem 9.34
I ii  I f  f
 f I i 14.


 3.5
i I f 4.0
This week’s Laboratory Experiment
M initial  0.471kg
M final  1.343kg
initial  248degrees/s
 final  64 degrees/s
L conserved?
M initial initial  2.039
M final  final  2.026
% difference  0.6
Problem 9.32
What is the angular momentum of a bar
rotating at 120 rpm. The bar rotates about its
center, has a mass of 500g and is 2 m long.
Problem 9.32
1
I  ML2  0.1667 kg m 2
12
  (120rpm/60s/min) * 2 rad/rev  4 rad/s
L  I   2.1 kg m / sec
2
Monday
Energy and Work
Reading: 10: 1-3
Problems: 9: 30, 32, 34, 35
A closed (isolated) system has a total energy E which
is constant, but the form of the energy can change.
For example, thermal, kinetic, chemical, …
We shall be concerned with the conversion of one
kind of energy into another and the exchange of
energy with the outside world.