162 Chapter 7 Length and Length-Related Parameters
As explained in Chapter 6, we have learned from our surroundings and formulated our
observations into laws and principles. We use these laws and physical principles to design,
develop, and test products and services. Are you observing your surroundings carefully? Are
you learning from your everyday observations? Here are some questions to consider: Have you
thought about the size of a soda can? What are its dimensions? What do you think are the
important design factors? Most of you drink a soda every day, so you know that it fits in your
hand. You also know that the soda can is made from aluminum, so it is lightweight. What do
you think are some of its other design factors? What are important considerations when design-
ing signs for a highway? How wide should a hallway be? When designing a supermarket, how
wide should an aisle be? Most of you have been going to class for at least 12 years, but have you
thought about classroom seating arrangements? For example, how far apart are the desks? Or
how far above the floor is the presentation board? For those of you who may take a bus to
school, how wide are the seats in a bus? How wide is a highway lane? What do you think are
the important factors when determining the size of a car seat? You can also look around your
home to think about the dimension length. Start with your bed: What are its dimensions, how
far above the floor is it? What is a typical standard height for steps in a stairway? When you tell
someone that you own a 32-inch TV, to what dimension are you referring? How high off the
floor are a doorknob, showerhead, sink, light switch, and so on?
You are beginning to see that length is a very important fundamental dimension, and
it is thus commonly used in engineering products. Coordinate systems are examples of
another application where length plays an important role. Coordinate systems are used to
locate things with respect to a known origin. In fact, you use coordinate systems every day,
even though you don’t think about it. When you go from your home to school or a grocery
store or to meet a friend for lunch, you use coordinate systems. The use of coordinate sys-
tems is almost second nature to you. Let’s say you live downtown, and your school is located
on the northeast side of town. You know the exact location of the school with respect to your
home. You know which streets to take for what distance and in which directions to move
to get to school. You have been using a coordinate system to locate places and things most
of your life, even if you did not know it. You also know the specific location of objects at
home relative to other objects or to yourself. You know where your TV is located relative to
your sofa or bedroom.
There are different types of coordinate systems such as rectangular, cylindrical, spherical,
and so on, as shown in Figure 7.1. Based on the nature of a particular problem, we may use one
or another. The most common coordinate system is the rectangular, or Cartesian, coordinate
system (Figure 7.1). When you are going to school from home or meeting a friend for lunch
you use the rectangular coordinate system. But you may not call it that; you may use the direc-
tions north, east, west, or south to get where you are going. You can think of the axes of a rect-
angular coordinate system as aligning with, for example, the east and north direction. People
who are blind are expert users of rectangular coordinate systems. Because they cannot rely on
their visual perception, people with a vision disability know how many steps to take and in
which direction to move to go from one location to another. So to better understand coordi-
nate systems, perform the following experiment. While at home, close your eyes for a few min-
utes and try to go from your bedroom to the bathroom. Note the number of steps you had to
take and in which directions you had to move. Think about it!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