How to explain pressure which produces gas on vessel walls

How to explain pressure which produces gas on vessel walls

Gas, as well as any other substance, is capable to put pressure. But, unlike solid bodies, gas presses not only on a support, but also on walls of a vessel in which is. What caused this phenomenon?


1. Within centuries was considered that air has no weight, and it can be felt, only when it moves (that is during wind). Such is there was a point of view of Aristotle, and very long it was the law for scientists.

2. In the middle of the 16th century Galilei's pupil Evangielista Torricelli, solving a problem with rising of water for fountains, found out that the air which was considered as weightless nevertheless has weight. As a result Torricelli invented the first mercury barometer by means of which he managed to measure the air pressure upon the Earth's surface and also calculated its density.

3. However the fact that air is attracted by the earth and therefore presses down, could not serve as the answer to all arisen questions. In particular, it became clear that pressure of air extends not only to what is under it, but also extensively at once, including up. The known experience with "the Magdebourg hemispheres" — the metal sphere from two halves between which of space pumped out air — showed that pressure of air can be quite enough that even several horses could not tear off a hemisphere from each other.

4. Subsequently it was revealed that not only air, but also in general any gases has such property. To find the answer to this riddle, other opening — the theory about the molecular structure of substance was required.

5. Molecules of which gas consists are not connected among themselves and are in random motion. They constantly hit against walls of the vessel filled with gas. These impacts are also gas pressure.

6. As gas is attracted by Earth, its pressure upon a bottom of a vessel is a little more, than on walls and a cover, but in most cases the difference is so small that it can be neglected. Only for all atmosphere of Earth in general the difference in pressure at a surface and at big heights becomes noticeable. In zero gravity the gas pressure upon all walls of a vessel is absolutely identical.

7. The size of pressure of gas depends first of all on the mass of this gas, its temperature and volume of a vessel. If temperature remains invariable, then increase in volume leads to reduction of pressure. With an invariable weight pressure grows together with growth of temperature. At last, at the constant volume the increase in weight leads to increase in pressure.

Author: «MirrorInfo» Dream Team