Question

Why can hand span or arm length not be used as standard units of length?

Answer 1

Hint: From person to person the physical features differ, some are tall and some are small. So, it would be unfair if everyone does not get equally due their physical differences.Let us give you a detailed description to get a clear idea.

Complete answer:
Length is a fundamental quantity and hence needs very accurate and precise measurement. Various instruments have been designed for accurate measurement.
But if one thinks that instead of using instruments why not use hand span and arm length for measuring the length. Let us see what will happen in such a case.
Suppose I want to perform an experiment where I want to measure the distance between two points which are at a certain distance away from each other. Two people are performing the experiment. One of them is taller and the other one is shorter. When we want the final results, we will actually see that both of them have different results. This is because the arm length and hand span vary from person to person.
As the result varies we won’t be able to understand which of them is the correct value and hence we will be unable to take any particular value and proceed further for the experiment. This is why hand span and arm length can not be used as standard units of length.

Note:
The standard unit of length is taken as a meter in SI units and we can convert a meter into various units like millimeters (mm), centimeter (cm), and kilometer (km). It is equal and fair throughout the world as it do not make any kind of differences on the bas9is of the physical features of a human body