Do you know how tall you are? What about your weight? And how long does it take to do certain activities? Measurements such as meter, kilogram, second and several others are very important for the study of physics. But, far beyond that, they are essential in our everyday life. We separate some curiosities and explanations of how the main units of measure were defined.

Meter (m)

Unit of measure of length, the meter derives from the Greek word “metron”, which means measurement. At first, the meter was defined as being one tenth of a millionth of the distance between the North Pole and the Equator. After that, for practical reasons, the meter became the distance between two thin lines marked on an iridescent platinum bar called the “standard meter bar.” This bar, which measures exactly one meter, was maintained in the International Agency of Weights and Measures.

With the development of science it was necessary to define a more accurate and secure way of recording the exact measurement of the meter. It was then that it was defined as the length of the path traveled by the light in the vacuum during a time interval of 1 / 299,792,458 of a second..

Second (s)

The time measure pattern is the second, which equates to the exact duration of 9,192,631,770 periods of radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium 133 atom.

The time measure had its beginning with the Egyptians, around the year 2000 a.C., still when the movement of the sun and the moon were taken as base to mark the passage of time. Obviously, this resource was not accurate and after many years the scientists realized that the terrestrial rotation should not be used as a reference for the division of time.

It was only with the development of atomic clocks that it was possible to have a more accurate measurement because they measure the time intervals through the oscillating frequency of the energy of an atom. To get an idea of the precision, the already constructed cesium-133 atomic clocks need approximately 6000 years to lose the accuracy of 1 second between them.

Kilogram (kg)

The kilogram is the standard mass unit in the International System of Units. It is defined by the mass of an equilateral cylinder of Iridium and Platinum, 39mm in height and in diameter. The International Prototype Kilogram has been stored since 1889 at the International Bureau of Weights and Measurements in Sevres, France, and its weight is also equivalent to one liter of water at its maximum density..

Since it is not possible to have access to the prototype, there is a second standard that defines the kilogram, which is 1/12 of the atomic mass of carbon-12 and is called u. Thus, 1u = 1.6605402 xkg, with an uncertainty of ± 10 in the last two decimal places.

Just as happen with the meter, some physical constant is being studied to redefine the kilogram, such as Planck’s constant, the mass of the electron and many others.

Did you like to know more about units of measurement? Keep an eye on our blog to find out many other curiosities in the world of physics.