Physicists Biographies

Length standard

By measuring a length using a tape measure we are determining how many times that length is greater than a chosen unit

As we already know, Physics is present in practically everything we do in our daily life. When we ride a bus, for example, we are immersed in various physical concepts, such as the maximum speed the bus reaches, the acceleration it acquires, the chemical energy of the fuel being transformed into mechanical energy, etc.

According to the above, some concepts and measures are used without realizing their importance. For example, to measure small distances, a ruler graduated in centimeters is used as a standard of measurement, but if the distance to be measured is very long, the meter, kilometer, etc. is used as the standard. The length measurement standard has always been measured in cm, m, km, etc.

What is known is that, in 1960, an international committee met to establish rules in order to define the standards of fundamental quantities. The system that was adopted after that meeting is a generalization of the metric system that became known as the International System of Units, whose abbreviation is (SI). In this adopted system, the units of mass, length and time are, respectively: the kilogram, the meter and the second.

Other fundamental units of the (SI) are the ampere, the kelvin, the candela and the mole. Therefore, these seven units were defined as the basis of the SI. But our object of study here is “length”.


From 1790, the decimal metric system was created, which sought to unify measurement standards and procedures. As a fundamental part of this new system, the meter , whose abbreviation is m , was defined as one ten-millionth of the distance between the North Pole and the Earth’s equator. Later, for practical reasons, this definition of the standard was abandoned and the meter came to be defined as the distance between two thin lines engraved near the ends of a platinum bar, called the standard meter, which was kept at the International Bureau of Weights and Measures.

In 1983, the need for precision in taking measurements reached such a point that even the krypton-86 standard became unsatisfactory and the SI adopted the current definition: the meter is the distance traveled by light, in a vacuum, during an interval of time equal to  a second.

The meter is a suitable standard only for not very extensive measurements. For much larger or smaller measurements, multiples and submultiples must be used, 

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