Understanding Measurement

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Many Properties Can be Measured

The world and the objects around us have many common properties. Some of the obvious ones are shape, size, weight, volume, duration & length. Humans used these properties, among other things, to identify, trade and barter. They bartered goods on the basis of quality, shape, size and weight. They also realized that it would be advantageous to convert these properties into numbers. The science of measurement developed from these ideas.

One of the earliest property to be measured must have been the passage of time in terms of days & years. Humans measured time with reference to the Moon & Sun.

Measurement of Physical Dimensions

The three basic physical dimensions are length, area and volume. These correspond to space occupied by physical objects in one, two & three dimensional space.

Each of these dimensions are independent of one another. None of the can be reduced to any of the other two.

But how come we get area by multiplying 2 linear dimensions and volume by multiplying 3 linear dimensions. This has been made possible by choosing appropriate measuring units.

The unit of length is the basic unit, which is defined as 1cm.

The unit of area has been defined in terms of a "square" whose sides equal the basic unit of length. The unit of volume has been defined in terms of a "cube" whose sides equal the basic unit of length.

Through this definition the area in "square units" can be got by a product of two linear lengths. Similarly the definition if volume in "cubic units" can be got by a product of three linear lengths.

Measurements Need a Number System

The development of measurements must have preceded and propelled the development of number systems. Counting was possibly the first measuring activity, possibly to get an estimate of their material possessions or to keep track of the passage of days.

Measurement Depends on Multiplicative Thinking

Measurement also depends on the idea of multiplicative thinking (Refer Chapter 18.4 & 18.5). To convert a property into numbers, a standard unit measure had to be adopted. The Kilogram for weight, Meter for length, Degrees for temperature are some examples of unit measures.

If we know the length of one meter, then the distance between 2 points can be expressed as a certain multiple number of meters. The number system gives us different types of numbers, like fractions &amp; decimals, to accurately express this distance.

Qualities Needed of Measuring Units

Further, any unit of measurement should be easily constructible as well as reliable. The unit should be such that it can be constructed anywhere using certain procedures.

The unit should also be reliable so that the numbers which result from the measurement are correct and easily verifiable. A weighing stone of 1 kg should be easily be "makeable" or available at all places and its weight should also be same as the standard.

Brief History of Measurement

The basic measurements that humans required were for discrete quantities, money, time, length, volume &amp; weight. Initially the units for all these measurements depended on events &amp; activities that humans could relate to.

Counting possibly developed to get a measure of discrete quantities. Time was based on the movements of the Moon &amp; the Sun. Length was based on the steps taken while walking. Volume depended on certain locally available standard sized containers and weight on certain stones. In the initial stages, groups of humans developed their own units as per their need and experience.

Slowly as groups got interlinked through trade &amp; social transactions, they evolved common units of measurement. Units also spread through wars for conquest of land & labor. The units used by the winners in their country were imposed on the conquered countries. Slowly units which were valid all over wider and wider areas were developed. Today we have units which have been adopted throughout the world.

The history of the development of various units of measurement is an interesting story of the problems faced by humans and their ingenuity in developing solutions to these challenges.

It is due to the development of accurate units of measurement that today design & manufacture of any product can be done in multiple locations and still adhere to single quality standard.

Some properties like temperature & speed became measurable with the advancement of science & technology.

Story of an Expensive Mistake

Confusion in the measuring system caused a costly mistake of $ 125 million! And that too in the 20th century!!

In 1999 the Mars Climate Orbiter crashed into Mars because the engineers who made the orbiter used English linear units while the NASA controllers thought they were in the metric system!

All things cannot be measured

We must also remember that there are many properties which we value that cannot be measured. Some examples are beauty, taste etc.

We will now see the history of development of some of these units briefly.

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