Measurements around us

Systems of units

Basic quantities are measured very often and similarly to history. With the rise of physics, more and more demands are placed on units and their definitions, not only in terms of accuracy, but also the possibility to reconstruct a certain unit, for example in our own laboratory on the basis of a generally valid definition.

What and how was it measured

The simplest and initially often used method of measurement was to compare the measured quantity with the most accessible model. That model was a part of the body or frequently used objects: thumb, footprint, step, buckets, barrels, cups. As the empire and kingdom grew, the need arose to establish uniform measures and weights for the needs of trade and the tax system. Even in a barter shop, sellers and buyers set a price - for example, how much wine I exchange for how much meat. And if the ruler set taxes and fees, he also tried to introduce uniform models, patterns of weights and standards - standards. In ancient Egypt, standards were available at the offices. Elsewhere, temples were a place for storing standards. The first standards were weights. A set of hematite weights from Mesopotamia from the period around 1700 BC has been preserved. However, the stone weights were quickly destroyed by use. Therefore, stone weights were replaced by metal ones - bronze, lead, later brass and iron were used. Weight was most often measured on isosceles scales. A weighed object was placed on one dish and a weight on the other. For example, Usir placed a heart on one bowl of scales and a pen, a standard, and the principle of truth and justice on the other. The length was usually measured with a rod of a given length. The complexity of the units has led to the need to limit the number of units and define their size. Later, the units were arranged and interconnected by conversion and definition relationships into measuring systems.

Units of length in Bohemia

The Middle Ages were a time of confusing units and their definitions. The smallest unit of length was the grain. The standard was a barley grain and its length was less than 5 mm. Laying four grains behind each other creates a finger that was less than 20 mm. Another unit was the palm, which had four fingers - which is approximately 79 mm. The forehead contained ten toes (197 mm), the three foreheads consisted of an elbow. The elbow has long been a basic unit of length and would deserve a separate chapter. It will be used in our territorythree main ramparts - from 1268 the Prague elbow or Czech elbow, from the middle of the 18th century the Viennese elbow and the Moravian elbow, the length of which was stabilized only in 1708. Their standards are preserved in the walls of various town halls throughout the Czech Republic. Each elbow had a different length: - Czech elbow = 59.3 cm, - Viennese elbow = 77.8 cm, - Moravian elbow = 78.9 cm. But there were many more elbows, at least fifteen were documented. Their length varied and ranged between 57 and 95 cm. The elbow was the most important measure of length until the introduction of metric measures in the 19th century. The multiples of the Czech elbow were as follows: - 1 earth string = 24 elbows, - 1 figure = 30 or 39 elbows, - 1 morning = 210 elbows (the area plowed by the farmer from morning to evening), - 1 rod = 1,050 elbows, - 1 rope = 12 rods = 12,600 elbows (acreage plowed by a farmer with a pair of oxen). Units of area, volume and weight were also defined. The situation in them was a little less confusing, but their transfer relations were complex. Only Maria Theresa succeeded in unifying the units into a comprehensive measuring system in our territory.

Specific systems in our territory

In order to consolidate the number of units and establish their mutual relationship, over time, systems of interconnected units were created. These systems significantly simplified the definitions of units and adjusted their mutual relations. Some systems have been used for a long time, some have left only a small trace in history. The Austrian measuring system was introduced in Bohemia on January 1, 1765. This system, sometimes also called the Vienna or Lower Austrian measuring system, established units of length, area, volume and weight. The basis of the system of lengths was the Viennese sah. However, the most important thing can be considered the provision of conversion ratios between units, which were used until the introduction of the metric system. To illustrate, let us mention some units of the Austrian measuring system:
- 1 point = 0.182 9 mm,
- 1 Viennese reach = 6 shoes = 189.648 4 cm,
- 1 belt dot = 0.000 345 233 m²,
- 1 morning = 5 754.64 m²,
- 1 bucket = 0.056 589 m³,
- 1 pharmacy pound = 0.420 045 kg.
So the nightingale, which brought a wine iron for the wedding, brought a bigger glass - glass with 3.58 dcl of wine. If someone is drinking beer, know that they are all cheating on us, because the oil should have 1.4 liters, the goblet should have 0.7 liters, and no less, as some beer producers try to tell us. From 1874 to 1889, the CGS system was used. Its name is derived from the names of the basic units centimeter, gram, second. The MKS system - meter, kilogram, second - began to be used in 1889. It is still used in some fields today, but was officially replaced in 1960 by the SI system. The Anglo-American measuring system, also known as the imperial system, contains standardized but irregular imperial units of SI.

The Anglo-American measurement system, also known as the Imperial System, contains standardized but irregular imperial units. The originator is Great Britain, which enacted the system in 1824, but by law of 1 October 1995 and with effect from 1 January 2000 introduced metric units with a few exceptions that allow the use of imperial units for specific purposes: – mile, yard, foot and inch (inch) for road markings and derived speed and distance measurements, – a pint for the dispensing of draft beer and must and for milk in returnable packaging , – an acre for land registration purposes, – a troy ounce for trading in precious metals. After the introduction of the SI system, most countries switched to the SI metric system. Yet there are still countries where the Anglo-American system of measure is the basic system of troops – Liberia, Myanmar (Burma), and, somewhat surprisingly, the US. However, it should be borne in mind that some units are different in the US than they were in the UK (short ton vs. long ton vs. metric ton). In addition, there are several different definitions for the seemingly same unit: the status mile (1,609 m) is different from the imperial nautical mile (1,853.2 m) and it is a little longer than the international nautical mile (1,852 m). The current and probably most perfect is the international system of SI units (from the French original Le Système International d'Unités). It is a system of interconnected units of physical quantities: meter (length), kilogram (mass), second (time), ampere (electric current), mol (substance quantity), kelvin (temperature) and candela (luminosity). Other units that depend on basic arithmetic are derived from these base units. The definition of these units is guaranteed by the International Bureau of Measures and Weights in Sèvres, France. In 1960, the SI system was declared internationally valid.

The definition of si base units is undergoing development, mainly due to the requirements for increasing accuracy of the unit definition – which is a significant problem for temperature and weight – and for the independence of the base units from each other, i.e. that one base unit is not defined by another base unit. Therefore, new definitions of base units were proposed in 2018.

Attractions

Weight is usually measured by weights. However, the problem is when it is necessary to measure the mass body in a state of unsuthed condition. The mass of bodies on Earth is measured by their weight, which depends on the mass acceleration. In orbit, however, the gravitational acceleration is compensated by the centrifugal force generated by the rotation of the station around the Earth. So how to measure mass in orbit and in space? The measurement uses the inertia properties of the bodies. Simply put, you attach a body (such as an astronaut) to the board, attach it with springs to the weight and give the cosmonaut a precisely given impulse of strength – you push it perpendicularly to the mat. The body (cosmonaut) starts thanks to the springs smite. And the frequency of oscillation is inversely proportional to the mass of the body (more precisely m = k (4π2f2)–1, where k is the coefficient of rigidity of the spring). So the cosmonauts attach themselves to the board, vibrate and learn their weight. The mass-measuring instrument is used on the ISS orbital station and was developed in Russia around 1976, first used at the Salyut-5 orbital station.

Literature: [1] Wikipedia [2] http://www.converter.cz/prevody/uk.htm