PHY122 Labs (
©
P. Bennett, JCHS) 1
10/25/06
PHY 122 LAB : Rotational Motion
Introduction:
In this lab we will see how a constant torque creates a constant angular
acceleration for a rigid body rotating about its CM. We’ll see that the moment of
inertia depends on the rotation axis for a given object. Finally, we’ll look at
rotational motion from an energy viewpoint. Applications of the moment of inertia
concept include the design of crankshafts, rotary rides at a fair, or the baton
twirling of a marching band leader. Text Reference: Young & Freedman 9.15.
Theory
A stone dropped into a well falls a distance Z = 0.5 g t
2
. If we convert this
equation to the angular domain, it says
Θ
= 1/2
α
t
2
. We study similar behavior in
this lab.
In more detail, a rigid object free to rotate about a principle axis with
moment of inertia I will accelerate according to
τ
= r*F = I*
α
,
eq. 1
where
τ
is the applied torque (given by the vector cross product of r and F), and
α
is the angular acceleration in rad/sec
2
. Recall
π
radian = 180 degrees. Take care
that
τ
,
α
and I are in consistent units. “ I ” is readily calculated for symmetric
objects, and has the form I =
β
MR
2
, where
β
is a dimensionless fraction (01) that
depends on the shape of the object and the rotation axis. A 3dimensional object
has 3 principal values of I, corresponding to 3 independent possible axes of
rotation. These values would all be the same for a sphere through its center, but
would all be different for a low symmetry object. Thus, for example, a rectangular
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '08
 fan
 Acceleration, Angular Momentum, Inertia, Kinetic Energy, Moment Of Inertia, Rigid Body, Rotation

Click to edit the document details