Physics 140 – Fall 2007
lecture #15 : 25 Oct
•
exam #2 is next Thursday, 1 November, 6:007:30pm
• covers Chapters 68
• practice exam on CTools site > Exams & Grading
bring
two
3x5 notecards, calculator, #2 pencils
•
review next Monday evening,
29 Oct
182 Dennison
8:009:30pm
Ch 9 topics:
• rotational kinematics
• rotational kinetic energy
• moment of inertia
Center of Mass of an extended, nonuniform object
x
com
=
1
M
dx dy
"
(
r
)
x
object
##
y
com
=
1
M
dx dy
"
(
r
)
object
##
y
M
=
dx dy
"
(
r
)
object
##
x
y
An object with surface mass density
!
(
r
),
shown here in 2D, has a total mass given
by the integral
Its center of mass is defined by integrals of
the massweighted positions:
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To describe rotational motion, we begin with the
angular position
"
(in
radians
) measured relative to
an (arbitrary) reference angle.
Rotational kinematics
"
0
3
#
/2
#
#
/2
really
2
n
#
,
n
=0,±1, ±2, ±3,…
O
A change in angular position,
$"
, during a
time interval
$
t
implies a nonzero
average
angular velocity
%
avg
=
$
"
/
$
t
A change in angular velocity,
$%
, defines
an average
angular acceleration
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 Fall '07
 Evrard
 Energy, Inertia, Kinetic Energy, Moment Of Inertia, Rigid Body, Rotation, Velocity, rotational kinetic energy

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