Составить план текста Physics measures such physical чшntitics as time, length, mass,
density, velocity, area, volume, tempcrature and cnergy. Different units of
length and mass exist. Nearly all ofthem are interrelated. Nowadays, three
main systems of measurement are widely used: the British system ofunity,
the metric system ofunits and the Intemational system of units (SI).
With а few exceptions, all the nations ofthe world use the metric system.
It is so easy that anyone who knows arithmetic can leam 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 intemationa1 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
Ьу ten. Therefore, the conversion to а higher quantity is done Ьу moving the
decimal point to the right to the required number of p1aces, and vice versa.
The idea of decimal system was realised only at the end of the 18th
century. In 1791, the French Academy of Science decided that the standard of length should Ье one ten-rnillionth 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 cublc metre appeared.
The main advantage of the system is that for shorter measurements the
metre is divided Ьу ten, so а decima1 system was used. Shorter units had
Latin preftxes and longer ones - Greek preftxes. 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 cublc centimetre of water at the temperature of 4 ·с (the temperature of its maximum
density). As we know, the name of this unit is gramme.
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The SI units is derived from the metric system and was intemationally
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 Ьу the units from this system.

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