Sharon Zhao
Partner: Sarah Brewington
TA: Keither Thrasher
Physics 107L-01
6/27/15
Rotational Motion
Introduction
Circular motion is the movement of an object along the circumference of a
circle or rotation along a circular path. In this lab, rotational motion was explored by
using a rotational motion apparatus to examine angular momentum, angular
acceleration from a torque, and moment of inertia. With experimenting with
rotational motion, we consider only rigid bodies. A rigid body is an object that
retains its overall shape, and in this lab disks were used. The rotational motion of a
rigid body occurs when every point in the body moves in a circular path along an
axis of rotation. The angular displacement (
ΔΘ
) is the angle the object turns and is
in units of radians. There are 360°, or 2
radians
π
in a circle. A radian can be found by
dividing the arc length by the radius. Angular velocity is the change in angular
displacement over time, defined by:
ΔΘ
/
Δ
t. Angular acceleration is the rate of
change of angular velocity,
α
=
Δω
/
Δ
t. Angular and linear quantities can be related
through 3 equations which are s=r
Θ
, v=r
ω
, and a=r
α
.
In previous labs, we have explored kinematic equations for bodies moving at
constant acceleration. There are very clear rotational counterparts for linear
displacement, velocity and acceleration, so we are able to define an analogous set of
equations for rotational kinematics. These include
ω
f
=
ω
0
+
α
t and
Θ
f
=
Θ
0
+
ω
0
t +
½
α
t
2
. Torque is a measure of rotational force and defined as force times the lever
arm,
Τ
= FL. The level arm is the perpendicular distance between the “line of action”
and the axis of rotation. If the definition of torque along with relationships between
linear acceleration and tangential angular acceleration are substituted into Newton’s
second law, we get
Τ
= I
α
. I, or mr
2
, is the moment of inertia of a point mass about
the center of rotation for a disk/cylinder. Angular momentum is rotational
momentum that is conserved and is a product of the moment of inertia and angular

velocity: L = I
ω
. The relevance to this lab is to explore these relationships between
angular velocity, angular acceleration, torsion, and inertia through various disks
spinning in a rotational motion apparatus.
Procedure
This lab was broken down into 3 experiments to explore different aspects of
rotational motion. The first explored angular momentum through the inelastic
sticking of two rotators. The masses and radius of two steel disks and one aluminum
disk was found using a weight scale and ruler. The steel disk with the large center
hole was placed at the bottom and the other steel disk was placed on top. We then
opened the file “rot_motion” on DataStudio. After turning on the air pump and