3
The Metric System
Functions
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3.2
Length
Copyright © Cengage Learning. All rights reserved.
Length
The basic SI unit of length is the metre (m). The height of a
door knob is about 1 m. (See Figure 3.1.) One metre is a
little more than 1 yd. (See Figure 3.2.)
The height of a doorknob is about 1 m.
One metre is a little more than 1 yd.
Figure 3.1
Figure 3.2
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Length
Long distances are measured in kilometres (km)
(1 km = 1000 m).
The length of five city blocks is about 1 km.
(See Figure 3.3.)
The length of five city blocks is about 1 km.
Figure 3.3
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Length
The centimetre (cm) is used to
measure short distances, such
as the width of the page
(about 21 cm), or the width of
a board.
The width of your small
fingernail is about 1 cm.
(See Figure 3.4.)
The width of your small fingernail is about 1 cm.
Figure 3.4
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Length
The millimetre (mm) is used to measure very small lengths,
such as the thickness of a sheet of metal or the depth of a
tire tread.
The thickness of a dime is about 1 mm. (See Figure 3.5.)
The thickness of a dime is about 1 mm.
Figure 3.5
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Length
Each of the large numbered divisions on the metric ruler in
Figure 3.6 marks one centimetre (cm).
The smaller lines indicate halves of centimetres, and the
smallest divisions show tenths of centimetres, or
millimetres.
Metric ruler
Figure 3.6
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Example 1
Read A, B, C, and D on the metric ruler in Figure 3.7.
Give each result in millimetres, centimetres, and metres.
Figure 3.7
Answers:
A = 12 mm, 1.2 cm, 0.012 m
B = 20 mm, 2.0 cm, 0.020 m
C = 25 mm, 2.5 cm, 0.025 m
D = 128 mm, 12.8 cm, 0.128 m
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Length
Choosing Conversion Factors
The correct choice for a given conversion factor is the one
in which the old units are in the numerator of the original
expression and in the denominator of the conversion factor,
or the old units are in the denominator of the original
expression and in the numerator of the conversion factor.
That is, set up the conversion factor so that the old units
cancel each other.
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Example 2
Change 3.6 km to metres.
Since kilo means 103 or 1000, 1 km = 1000 m. The two
possible conversion factors are
and
Choose the one whose numerator is expressed in the new
units (m) and whose denominator is expressed in the old
units (km). This is
conversion factor
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