Dimensions of a Solid Body

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Distances of solid objects, for example the diameter of an object, cannot be measured directly with an ordinary scale. For such measurements as this, calipers are employed. These consist of a pair of hinged curved steel jaws, as shown in Fig. The jaws are closed until they both touch the object in the position for which a measurement is required and the distance between them is afterwards measured on a suitable scale.

7. Make up and write 5 questions using the words given in the table:

What system What What units

was used was distributed is used was intended were obtained

to be a standard of length. in our country. by multiplying or dividing the metre by tens. universally.

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8. Copy these sentences putting "metre", "alloy", "obtain, "designed'', "advantages", "length", "resistant" in the blanks:

1. The French government made an entirely new standard of ... the metre. 2. The ... was intended to be the unit length. 3. A bar of a platinum-iridium ... is very ....to corrosion in the earth's atmosphere. 4. The other units were by dividing and multiplying the metre by tens. 5. The new system of measurements was ... for simplicity. 6. We were quick to see the ...of the metric system.

Laboratory Exercises

9. Listen and practise the pronunciation of the following words:

eighteen, fifteen, seventy, sixty, measurement, government, resistant, corrosion, originally, mainly, closely, entire ly, quickly.

10. Listen and repeat in pauses:

The system of measurement based on the metre is the Metric System. It was designed for simplicity. The other units are obtained from the metre by multiplying or dividing by tens. The standard metre, a bar kept at the International Bureau, is now defined in terms of the wavelength of a parti-ular kind of light.

11. Listen to these questions on the above text and answer them:

1. What is the Metric System? 2. How are the other units obtained from the metre? 3. Where is the standard metre kept? 4. How is the standard metre defined?

12. Ask questions using the model.

Mоdel : The standard metre was made by the French government during the eighteenth century When was the standard metre made?

1. The present standard was made in 1875. 2. The Metric System was set up in the eighteenth century. 3. An Interna tional Bureau was set up in 1875. 4. The Metric System was used by our country closely after the Great October Socialist Revolution. 5. The new State Standard (SI) was adopted 1961.

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13. Suggested topics for oral narration:

1. What is the Metric System? In what is its simplicity?

2. Describe how yon would try to measure as possible: a) the length of a table, b) the diameter of a round body.

Additional Material

Read the text and get its central idea. Write sentences that best tell the central idea.

Origin of the Metric System

The metric or decimal system is the international system of measures and weights based on the metre and the kilogramme. That system was recognized by all the countries of the world except England and America.

Previously to the introduction of the metric system, the terms "foot" and "pound" that were used for hundreds of different weights and lengths, caused serious difficulties in the commercial relations among various countries.

The idea of securing a uniform system of measures and weights dates from long ago, but it was only at the close of the 18th century that it was realized. In 1791 a commission set up by the French Academy of Science recommended that the standard of length should be one ten-millionth part of the distance from the Earth's Equator to the North Pole measured along the meridian.

The two French mathematicians who were charged with the task of defining these units, took the distance from the North Pole to the Equator, on a line running through Paris, and divided it into ten million equal parts. One of these parts they called a metre.

For shorter measurements they divided the metre by ten or used the decimal system. For longer things they multiplied the metre by tens. Whenever they divided, they did it in Latin, and whenever they multiplied, they did it in Greek. Thus "millimetre" is Latin for "a thousandth of a metre", while "kilometre" is Greek for "a thousand metres" and so on with the other terms. It was easy to use the same metre for volume. The weight of one cubic centimetre of Water was called a gramme, one thousand grammes making

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a kilogramme. Thus the metric or decimal system was created, that has found such a wide application in the world to-day.

UNIT 4