Body
parts and senses used for measurement
Since
ancient times, people used their senses and body parts
to measure various things. They did this because it became
necessary for them in their daily life to deal with other
people. Let us find out how senses and body parts help
us in measurement.
Contents
(a)
Use of our body parts and senses for measurement
(b)
Use of body parts for measurement
(c)
Limitations of our senses and body parts
(a)
Use of our body parts and senses for measurement
We
have five senses, which help us to find out about the
things around us. These senses are seeing, hearing, smelling,
tasting and touching. For example, if we see a tall and
a short building or a tall and short person we can feel
the difference in their heights. Similarly, if we touch
a body we can feel the hotness or coldness of the body.
Thus, our senses do help us to guess or estimate the height,
length and hotness or coldness of a body and other things
around us. Here, estimation means a rough measurement
made by our senses.
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(b)
Use of body parts for measurement
In
ancient days, long before measuring instruments were invented,
people actually used different parts of their body to
measure length. Figure 1.1 shows various parts of our
body, which were used and can still be used to carry out
various measurements. But since these measurements are
dependent on the size of the person, they may vary from
person to person. The length of the cubit, for example,
depends on the arm length of the measurer. Thus, cubits
had different lengths. To have a better understanding,
let us perform an activity.
Fig. 1.1 Use of body parts for measurement
Use
of body parts for measurement
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(c)
Limitations of our senses and body parts
Though
we use our senses and body parts for various measurements,
we cannot trust them to measure exactly and accurately.
Can you depend on your eyes to judge accurately the height
or lengths of different objects? Look at figure 1.2a.
Which circle is larger-A or B? Well, both are of the same
size. Larger circles around the central one make it appear
smaller. Small circles around the central circle make
the other appear larger.
Fig. 1.2 Limitations of our senses and body parts in measurement
There are many more such instances where objects can fool
our eyes. Now look at figure 1.2b and tell which line
segment is larger. Verify your estimation by measuring
each line segment with the help of a scale.
In the above mentioned cases we tried to guess the length
or size by seeing i.e. tried to give an estimate, which
may or may not be correct. Thus, the use of senses or
body parts for measurement does not provide
l accuracy of measurement,
l reliability of measurement,
l uniformity of measurement,
The limitations of the use of senses and body parts have
made us to develop some devices and instruments for accurate
measurements.
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