Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

190 Chapter 7 Length and Length-Related Parameters

EXAMPLE 7.5 Calculate the second moment of area for a 5-cm-diameter shaft about thex–xand they–yaxes

shown in Figure 7.25.

Finally, it is important to emphasize the fact that all physical variables discussed in this chap-

ter are based on the fundamental dimension length. For example, area has a dimension

of (length)

2

, volume has a dimension of (length)

3

, and the second moment of area has a dimen-

sion of (length)

4

. In Chapter 8, we will look at time and time-and-length-related quantities in
engineering analysis and design.

Summary

Now that you have reached this point in the text

• You should understand the significant role the fundamental dimension length plays in engi-
  neering problems. You should also realize the importance of area and volume in engineering
  applications.


• You should have developed a “feel” for the relative magnitude of various length units, area
  units, and volume units.


• You should know the difference between the actual size and a nominal size of objects.


• You should know how to measure areas and to approximate planar surfaces using the trape-
  zoidal rule.


• You should have a good understanding of the physical significance of the second moment of
  area in structural analysis.

IxxIyy

1

4

pR

4



1

4

1 3.14152a

5 cm

2

b

4

30.7 cm

4

x x

y

y

R

■Figure 7.25 The shaft in Example 7.5.

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