Page 4 - Length

4.2 Standard units of measurement

Today, in many parts of the world, we use the same system of
units to measure length. That makes it possible for us to tell
other people how long an object is. The system is called the
International System of Units (SI).

We call these units the standard units. They are the same
everywhere in the world where they are used.

1. What is the difference between a standard unit and a unit that
is not standard? Talk about this with a classmate.

We use different instruments that are marked in standard units
to measure the length of objects. Here are two of the instruments
that we use to measure shorter lengths.

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Ruler

Measuring tape

Your teacher can show you another commonly used ruler. It is
1 m long and it is called a metre stick.

In 1793, people in France decided that they would use the
metre (m) as the standard unit for length. One metre is the
standard and the other units are named for how they relate to the
metre.

A centimetre (cm) is one of the 100 cm = 1 m
parts if 1 m is divided into 100 equal
parts.

There are 100 cm in 1 m.
Centi- in centimetre means hundredth.

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