PHY 221 Lab 9
Torque and Rotation
Leader:
Critic:
Scribe:
Goals
:
Rotation is a rich subject, and we only scratch the surface of it in PHY 211 and 221. Rotary motion
is like translational motion in many ways. Just as we describe ordinary translational motion by the
kinematic quantities
position (x), velocity (v=dx/dt) ,
and
acceleration (a=dv/dt)
, rotation is
described by the kinematic quantities
angular position (
), angular velocity (
d
/dt
,
and
angular acceleration (
d
/dt
)
. Just as a force is needed to change the state of translational motion
nd
Law
F=ma
), something called a
torque
(
) is needed to change the state of
nd
Law,
I
. Here
I
is
moment of
inertia
. Moment of inertia is equal to
m
i
l
i
2
, where the sum is over all mass elements of the extended
object (
m
i
), and
l
i
is the distance of the mass element to the axis of rotation.
There is also
angular momentum (L=I
)
nd
Law can be written as&&&
=
d
L
/dt, we see that angular momentum is
conserved
(L=const) if net external torque on the system is
zero (
=0).
momentum.
Materials:
Balance, Screw drivers, Wrench, Hammers
Flywheels
Rotating platform and set of dumbbells
Gyroscope
Since in many cases we have only one or two versions of each setup, you
and your group will have to rotate to the various pieces of equipment.
Do
the various activities in whatever order is convenient
.
Page 1 of 10
PHY 221 Lab #1: Introduction to Measurements
12/28/2009
http://physics.syr.edu/courses/PHY221.07Spring/manuals/torqueandrotation.html
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1.
Balance
Weigh 1kg mass using a balance (Note: our mass sets are not very precise).
Make a sketch of the key parts of a balance. Measure the key dimensions and label them on
your sketch.
What condition do you look for when you say it is balanced? Which angular quantity is
constant? zero?
Angular position
Angular velocity
Angular acceleration
nd
Law in
angular form in your argument)
The net torque on the balance beam comes from the torque generated by the mass being
measured and from the torque by movable masses on the beam.
Torque can be calculated with respect to different reference points. It makes sense to
calculate torque with respect to a point the rigid body can rotate about. For example, in case
of the balance beam, the suspension point.
Torque from the force
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 Spring '10
 TOMASZSKWARNICKI
 Angular Momentum, Rotation, 1 kg, 1Kg, 90 degrees

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