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Expansion of Gases

Just as we can cool a gas by (make, making) it do work, so we can heat it by (do, doing) work upon it. Suppose, instead of letting the gas push the piston we (apply, applying) power to the piston and make it push the gas. This speeds up its molecules and makes it hot. It follows, then, that if we (compress, compressing) a gas it becomes hotter. The (better, best) example of this is seen in a bicycle pump, which becomes very (warm, warmest) when a tyre is inflated. Yon might think this was due to the friction of the piston, but if you try working the pump without a tyre, you will find it does not heat up (noticeable, noticeably).

The expansion of a compressed gas is used in driving steam-engines, petrol-engines, hot-air-engines, etc.

Gases expand very (larger, largely) when they are heated. We saw that a cubic foot of steel expanded by 5 cubic inches when heated from 0 °C to 78 °C, while a cubic foot of alcohol expanded 150 cubic inches over the same range. A cubic foot of air when heated from 0 °C to 78 °C expands by no less than 493 cubic inches. An interesting thing is that all gases expand to exactly the same extent when heated under the same conditions, which is by no means true for liquid or solids. When a liquid or solid is heated and expands there are two forces at work. The molecules are speeded up and so tend to swing in (bigger, biggest) orbits or to get further from each other. This effect is the same for all solids or liquids. But the attraction of the molecules opposes this effect; consequently substances whose molecules attract each other (strong, strong­ly) will expand little and vice versa. But the molecules of gases are too far from each other to attract each other appreciably, so the effect of heating them is simply to increase the speed and energy of the molecules and make them bounce off each other (hard, harder) and so fly farth­er apart. As the same rise of temperature means the same increase of energy, all gases expand (equal, equally).

The expansion of gases is very large, but it is not very useful for measuring temperatures because they expand and contract not only when the temperature alters but also when the air pressure alters. The expansion of a gas is sometimes used to measure rather high or very (low, lower) temperatures and also for very accurate work. An air thermometer is rather a difficult affair to handle, and it is used only in the laboratory [2, С. 73].

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Read the text. Find the definitions of Brownian motion and specific heat of a gas. Summarize the text into 8 main sentences.

<== попередня сторінка | наступна сторінка ==>
Liquefaction of Gases | Kinetic Theory of Gases

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