BACKGROUND:
Students traditionally
learn how to measure straight items, but most objects in the real world
are curved. Metrology is the science of measurement and is a fundamental
tool in all aspects of science and everyday living. Imagine a carpenter
who doesn't know how to measure? Lord Kelvin (England) once stated
"when you can measure what you are speaking about and express it in numbers,
you know what you are speaking about and you know something about it; but
when you cannot measure it, when you cannot express it, your knowledge
is of a meager and unsatisfactory kind".
Measurement involves a comparison
of an unknown to a known quantity. These known quantities are actually
set standards derived by international agreement. There is no magic
in a meter, a yard, a foot, or a kilometer. These lengths were arbitrary
to start with and are subject to change. They were used as a way
to keep track of distance. For instance, from 1889-1960, a meter
was the distance between 2 marks on a metal bar. Now it pertains
to a certain number of wave lengths in a particular spectrum line.
Students should also be aware
that measurement is not always accurate, and many scientists take a margin
of error into consideration. The purpose of this measurement exercise
is to review how to measure straight and curved items. Students
will practice predicting or estimating what each length will be. This skill
needs to be practiced since many times a ruler is not available. Many carpenters
can accurately predict measurements without a ruler because they practice
linear measuring skills over and over.
PROCEDURE:
- Use the worksheet
to guide the activity.
- Discuss how to measure curved
surfaces by taking a string and calibrating the length (like a tape measure).
Another method is to measure the object first with the string, then measure
the length of string.
- Ask students to get
a partner and work their way through the worksheet following the directions
carefully for Exercises 1-3. In Exercise 3, make sure that students
realize that they measure with a string an object that is round, and then
measure the length of the string to a ruler. If you have a tape measure,
that will find the length without measuring the string.
- When students are finished,
go over the results and guide them through Exercise 4. The answers are
ft. = feet; in.= inches; cm. = centimeters; yd. = yard; mm. = millimeters;
km. = kilometers; m. = meters; mi. = miles.
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