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

accuracy more clear. However, if the number was initially expressed as 1500.0, then it has four

significant digits and would imply that the accuracy of the number is known to 1/10000.

Addition and Subtraction Rules When adding or subtracting numbers, the result of the calculation

should be recorded such that the last significant digit in the result is determined by the posi-

tion of the last column of digits common to all of the numbers being added or subtracted. For

example,

The numbers 152.47 and 3.9 have five and two significant digits, respectively. When we add

these two numbers, the calculator will display 156.37; however, since the first column after the

decimal point is common to these numbers, the result should be recorded as 156.3.

Multiplication and Division Rules When multiplying or dividing numbers, the result of the calculation

should be recorded with the least number of significant digits given by any of the numbers used

in the calculation. For example,

In the above example, the number 152.47 has five significant digits and the number 3.9 has two

significant digits. Therefore, the result of the calculations should be recorded with two signifi-

cant digits, because the number 3.9 used in the calculations has the least significant digits.

Finally, it is worth noting that in many engineering calculations it may be sufficient to

record the results of a calculation to a fewer number of significant digits than obtained follow-

ing the rules explained previously. In this book, we present the results of example problems

with two or three decimal points.

6 6..7 7 EEnnggiinneeeerriinngg CCoommppoonneennttss aanndd SSyysstteemmss

Every engineered product is made of components. Let us start with a simple example to dem-

onstrate what we mean by an engineering system and its components. Most of us own a win-

ter coat, which can be looked at as a system. First, the coat serves a purpose. Its primary function

is to offer additional insulation for our bodies so that our body heat does not escape as quickly

and as freely as it would without protective covering. The coat may be divided into smaller

components: the fabric comprising the main body of the coat, insulating material, a liner,

threads, zipper(s), and buttons. Moreover, each component may be further subdivided into

smaller components. For example, the main body of the jacket may be divided into sleeves,

5.9 10 39 1 However, the result should be recorded this way. 2

2

594.633 39.0948717949 1 Your calculator will display. 2

3.9 3.9

152.47 or 152.47

156.3 127 1 However, the result should be recorded this way. 2

156.37 127.853 1 Your calculator will display. 2

3.9 5

152.47 or 132.853

146 Chapter 6 Fundamental Dimensions and Units

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