Physics measures such physical quantities as time, length, mass, density, velocity, area, volume, temperature and energy. Different units of length and mass exist. Nearly all of them are interrelated. Nowadays, three main systems of measurement are widely used: the British system of unity, the metric system of units and the International system of units (SI).
With а few exceptions, all the nations of the world use the metric system. It is so easy that anyone who knows arithmetic can learn it quickly. Before the introduction of the metric system (metre-kilogram-second), the British foot- pound-second system was widely used. But the latter system (which is still in use in Great Britain and the USA) was very complicated and caused serious difficulties in the international trade. For example, in the British system 1 mile is equal to 1760 yards, 1 yard - to feet and 1 foot- to 12 inches. This means that it's very difficult to convert units. But in the metric system each unit is а multiple of the following lower unit bу ten. Therefore, the conversion to а higher quantity is done bу moving the decimal point to the right to the required number of places, and vice versa.
The idea of decimal system was realized only at the end of the 18th century. In 1791, the French Academy of Science decided that the standard of length should bе one ten-millionth part of the distance from the Equator to the North Pole. The two French scientists charged with the task took this distance on а line running through Paris and divided it into 10 000 000 equal parts. They called one of the parts а metre ('measure'), which became the main unit. Metre was also used to measure area and volume. Thus а square metre and а cubic metre appeared.
The main advantage of the system is that for shorter measurements the metre is divided bу ten, so а decimal system was used. Shorter units had Latin prefixes and longer ones - Greek prefixes. So, 'millimetre' is Latin for 'а thousandth part of а metre' and 'kilometre' is Greek for 'а thousand metres'.
As for the unit of mass, it was defined as the mass of а cubic centimetre of water at the temperature of 4 degrees (the temperature of its maximum density). As we know, the name of this unit is gramme.
The SI units is derived from the metric system and was internationally accepted in 1960. Besides metre (m), kilogram (kg) and second (s), its basic units are Kelwin (К), ampere (а), mole (mol), and candle (cd). This system was introduced in our country in the 1960s and every day we measure things bу the units from this system.
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Continue the following statements.
1. The British system of units, the metric system of units and the
International system of units (SI) are ...
2. Everyone who knows arithmetic can ...
3. Before the introduction of the metric system ...
4. The conversion to а higher quantity in а metric system is done ...
5. In 1791 the French Academy of Science decided ...
6. The two French scientists took this distance ...
7. Metre was also used to measure ...
8. The main advantage of the metric system is ...
9. The unit of mass was defined ...
10. The SI system is derived ...
