223
Angular Accelerations
In the previous section, we defined angular speed and its importance in engineering applications.
We now define angular acceleration in terms of the rate of change of angular velocity. Angular
acceleration is a vector quantity. Note also that similar to the relationship between the
average acceleration and instantaneous acceleration, we could first define an average angular
acceleration as(8.17)
and then define the instantaneous angular acceleration by making the time interval smaller and
smaller in Equation (8.17).Example 8.6 It takes 5 s for a shaft of a motor to go from zero to 1600 rpm. Assuming constant angular accel-
eration, what is the value of the angular acceleration of the shaft?
First, we convert the final angular speed of the shaft from rpm to rad /s.1600 a
revolutions
minutes
ba
2 p radians
1 revolution
ba
1 minute
60 seconds
b167.5
rad
s
angular acceleration
change in angular speed
time
Nahid Afsari
My interest in engineering has taken me
from building a spaghetti bridge in high
school to designing the reconstruction
of a real “spaghetti bowl”— downtown
Milwaukee’s Marquette Interchange. The
transition from pasting pasta to designing
part of an $810 million project for the Wisconsin
Department of Transportation has been rewarding. As
a structural engineer at CH2M HILL assigned to the
replacement of the high-profile complex interchange
that links three interstate highways near Marquette Uni-
versity, I design bridges for the project’s half-mile-long
east leg. My diverse experience also includes a “low-
profile” project, which calls for a highway undercrossing
that enables a threatened species of snake to safely get to
the other side of the road.
Ever since I can remember, I have been intrigued
by puzzles, how things work, and how pieces fit together
to make something whole. I enjoy problem solving and
teamwork to reach a goal, and an engineering careerenables that in a big way. One of the nicest things about
civil engineering is seeing the finished product and
knowing that people in the community are benefiting
from what I have designed. Besides engineering’s appeal
to my basic nature, the fact that my father and my older
brother are engineers and have thoroughly enjoyed their
work also influenced my career choice.
The biggest challenge I faced as an undergraduate
student at the University of Wisconsin —Madison was
balancing study time with the rest of my activities. On
top of being a full-time student on track to finish my
engineering degree in four years, I was on the women’s
intercollegiate soccer team and a member of the
American Society of Civil Engineers student chapter
(participating in several regional and national concrete
canoe competitions). My busy schedule taught me a lot
in terms of how to prioritize tasks and manage time
effectively. Those lessons have proven to be invaluable in
my professional life, especially in the fast-paced and
demanding atmosphere of a major project office.Professional Profile
Source:Courtesy of Nahid Afsari
Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀圀圀圀⸀夀䄀娀䐀䄀一倀刀䔀匀匀⸀䌀伀䴀