Story of Measurement 2

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Weight– was originally defined in Britain in terms of ounces &amp; pounds. The origin of these terms is not very clear. Other cultures must have had their own units.

Later the unit of weight was defined in terms of the weight of a unit volume of pure water. Hence the weight of 1 Cubic Cm (which was also called MilliLitre) was defined as 1Gram.Water was taken as the reference because of its universal availability.

The interconnection between volume &amp; weight units can easily be remembered as shown in the following example.

A litre can be imagined as the volume of a cube whose sides are 10 cms each. Each cc of water weighs 1gm. There are 1000 cc&rsquo;s in a litre. Hence a litre of water weighs 1 Kg.

Hence 1cc is also called a Milli Litre (ml) (1/1000th of a litre).

1 cubic meter has 1000 litres. 1 cubic metre of water weighs 1000 kgs or 1 Tonne.

The complete angle was related to the movement of the Earth around the Sun in a year. Possibly the complete angle was seen as made of 360 degrees since the year was calculated as consisting of 360 days.

Angles are also measured in radians. In radians, a complete angle is 2&pi; and the sum of the angles of a triangle is &pi;.

The Very large &amp; the Very Small

With the advancement of nuclear science &amp; astronomy and digital technology, there has been a need to develop units which can be used to measure very large &amp; very small distances and time periods. The International System has also been extended to accommodate these needs.

These units have been described in an earlier chapter 17.9 on &ldquo;Decimals in Daily Life&rdquo;

Derived Units

Derived units are built from the basic units and they usually reflect the &ldquo;rate&rdquo; between 2 different kinds of units.

Speed = Distance/ Time – Rate at which the distance changes w.r.t time

Density = Weight / Volume – Rate at which the wright changes w.r.t volume

< 24.3 Measurement of Time | Topic Index | 24.5 International System of Measurements >