Continue the following statements.
1. The British system of units, the metric system of units and the nternational system of units (SI) are ...
2. Everyone who knows arithmetic can ...
3. Before the introduction of the metric system ...
4. The conversion to higher quantity in a 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 ...
Вот текст:
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 a 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 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 by ten. Therefore, the conversion to a higher quantity is done by 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 be 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 a line running through Paris and divided it into 10 000 000 equal parts. They called one of the parts a metre ('measure'), which became the main unit. Metre was also used to measure area and volume. Thus а square metre and a cublc metre appeared.
The main advantage of the system is that for shorter measurements the metre is divided by ten, so a decima1 system was used. Shorter units had Latin preftxes and longer ones - Greek preftxes. So, 'millimetre' is Latin for 'a thousandth part of a metre' and 'kilometre' is Greek for 'a thousand metres'
As for the unit of mass, it was defined as the mass of a cublc centimeter of water at the temperature of 4 ·с (the temperature of its maximum density). As we know, the name of this unit is gramm.
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 by the units from this system.
2. When I got to the cinema, the film had started.
3. The students entered the classroom five minutes after the bell had rung.
4. After she had locked and bolted all the doors, she went to bed.
5. The students did the exercise very well after the teacher had shown them how to.
6. The little boy told a lie five minutes after he had promised to tell the truth.
7. When the plane landed, the sun had set.
8. She felt sick after she had eaten a whole box of chocolates.
9. After the doctor had examined the child he had a talk with the mother.
10. When I called on my friend, he had gone out.
11. Mary had finished her homework when her father came home from his office.
12. I threw away the newspaper after I had read it.
13. After she had spent all her money she asked her father to help her.
14. The teacher gave back the exercise-books after he had corrected them.
15. The sun had risen when the farmer started work.