Three states of matter

We know that the cohesion between the molecules of a solid body is very great. A solid body retains its form.

When a solid body is heated, the motion of its molecules incomes more rapid. The cohesion among the molecules weakens; the body expands on heating. On further heating, the movement of the molecules becomes still more rapid and the attraction between them diminishes.

Finally, when the motion of the molecules has attained some velocity, the molecules begin to move among other molecules in various directions, chaotically, in disorder. The co­hesion has become very much weaker. The body is no longer a solid. It has been transformed into a liquid; it has melted.

On cooling, the above described phenomena occur in exactly the reverse order.

At some temperature the density is so great that the liquid becomes a solid body.

During melting the bond between the molecules becomes considerably weaker than in the solid body. In order to sepa­rate the molecules from one another, it is necessary to over­come the attraction between them, it is necessary to perform work to destroy the bonds between the molecules. Overcoming the attraction, the molecules situated on the surface of a liquid escape from the liquid into the air. These are molecules of vapour.

The higher the temperature of the liquid, the greater the number of molecules escape from the liquid. Hence, when a liquid is heated, the rate of evaporation is increased.

The larger the surface of the evaporating liquid, the greater the number of molecules that can escape from the liquid at the same time.

The velocity of the molecules increases in proportion to the temperature of the liquid and, finally, the velocity becomes so great that the formation of vapour goes on not only on the surface but through the liquid.

Liquids whose molecules are weakly attracted to one an­other are easily evaporated. Such liquids are called volatile liquids. Less energy is required for their evaporation.

Attraction between molecules of vapour is practically non­existent. As a result of this, molecules of vapour move in all directions, collide with one another and occupy a vast volume in comparison with the volume of the liquid from which they were formed.

The state of substance depends on the velocity of its mole­cules.

Render and memorize the following words and word-combinations:

1.cohesion –

2.a solid body –

3.to heat –

4.rapid –

5.to weaken –

6.attraction –

7.to diminish –

8.velocity –

9.to melt –

10.vapour -

Answer the questions:

1.What is the cohesion between the molecules of the solid body?

2.When does the motion of the molecules become more rapid?

3.When has it been transformed into the liquid?

4.What are the molecules of vapour?

5.What liquids are easier evaporated?

TEXT 6

Read and translate the following text:

Electricity. Electrical engineering the nature of electricity

The ancient Greeks knew that when a piece of amber is rubbed with wool or fur it achieves the power of attracting light objects. Later on the phenomenon was studied, and, the word electric, after the Greek word "electron", meaning amber was .used. Many scientists investigated electric phenomena, and during the nineteenth century many discoveries about the nature of electricity, and of magnetism, which is closely relat­ed to electricity, were made. It was found that if a sealing-wax rod is rubbed with a woolen cloth, and a rod of glass is rubbed with a silken cloth, an electric spark will pass be­tween the sealing-wax rod and the glass rod when they are brought near one another. Moreover, it was found that a force of attraction operates between them. An electrified sealing-wax is repelled, however, by a wax rod, and also an electrified glass rod is repelled, by a similar glass rod.

The ideas were developed that there are two kinds of ele­ctricity, which were called resinous electricity, and that opposite kinds of electricity attract one another, whereas similar kinds repel one another.

Memorize the following words and word-combinations:

1.amber – янтар

2.to rub – терти

3.wool – шерсть

4.fur – мех.

5.аttract – притягувати

6.investigate – досліджувати

7.relate – повязувати

8.spark – іскра

9.оpposite – протилежні

10.similar - подібні

Answer the questions:

1.What did the ancient Greeks know?

2.What word was used for the word of “electric”?

3.Who investigated this phenomena?

4.Are there two kinds of electricity?

5.Were they called resinous electricity?

TEXT 7

Read and translate the following text: