The reason is, that the particles of air or gas, far from being under the influence of cohesive attraction, like solids or liquids, are actuated by a powerful repulsion for each other. The addition of heat mightily enhances this repulsive tendency, and causes great dilatation.
The rate of the expansion of air and gases from increase of temperature, was long involved in considerable uncertainty. This arose from the neglect of the early experimenters to dry the air or gas upon which they operated.
The presence of a little water by rising in the state of steam into the gas, on the application of heat, occasioned great and irregular expansions.
But in , the law of the dilitation of gases was discovered by M. Gay-Lussac, of Paris, and by Dr. Dalton, of England, independently of each other. It was discovered by these philosophers, that all gases experience the same increase in volume by the application of the same degree of heat, and that the rate ot expansion continues uniiorm at all temperatures. Dalton confined a small portion of dry air over mercury in a graduated tube.
He then placed the whole in circumstances where it was unilormly heated up to a certain temperature, and observed the expansion. Gay-Lussac's apparatus was more complicated bub calculated to give very precise results, He found that 1, volumes of air on being heated from 32 to , became , which agreed very closely with Dalton's result. The still more recent and exact researches of Magnus and of Regnault, give as the expansion of air from 32?
Geezer Naked Science Forum King! As Sophiecentaur says, it's because of the kinetic energy of the gas molecules. It might also help to turn the question on it's head. As in, why does air heat up when it is compressed? The air contains a certain number of molecules. The molecules have a certain amount of heat energy in the form of kinetic energy. When the air is compressed the total heat energy now occupies a smaller volume.
Unless heat is rapidly removed while the air is being compressed, the air's temperature has to increase because the heat energy per unit volume is increasing. The expansion process is the exact opposite, so unless heat is added while the air is expanding, the temperature has to decrease.
The compression heating effect can be quite dramatic. Before the development of matches, air compression devices were used for lighting fires. Hi John we did this experiment as a Kitchen Science. You are therefore adding energy to the rubber so it becomes hotter. When you let you the process is reversed. Now the rubber does work pulling the straightened chains back to their initial compact configuration.
Since the elastic has done work, using energy, the rubber must lose energy in the process and therefore it becomes colder. In the link above Dave's put a nice interactive animation that enables you to demonstrate this for yourself.
That's a fun computer model. Clever old Dave. I'm still not clear about this, though? Are you saying that something will necessarily get warmer if you put energy into it? Will a wrist watch get warmer if you wind it up or a jar of pickles if you lift it on to a higher shelf? Sorry for highjacking your thread, mike2niner4. But this is a vaguely similar question to the original one, which I think has now been answered by Geezer's very plausible sounding explanation.
Ahhh, I've heard about adiabatic cooling in respect of meteorology. Moving air hits a mountain or hill and is forced upwards. With higher altitude comes lower pressure and the air expands and cools.
Cold air holds less water vapour than warm air and at some point up the mountain the air will reach it's dew point the water saturation point of the air and the water vapour will condense out as cloud.
This is why cartoon mountains are often drawn with a cloud circling it's peak. Turveyd Jr. Heat is basically the average speed of a single gas molecule multiplied by all the molecules in the gas. Heat can be seen as the total amount of energy of all the molecules in a certain gas.
Spacecraft designers sometimes need to cool equipment to very cold temperatures. They need to do this because they want to look at infared light. The reason why the equipment needs to be cooled to very low temperatures is that infrared radiation is generated by heat. If the camera which you are watching is warm, then it will be generating "light" and will not be able to see into space.
All the camera will see is its own warmth and therefore cannot look at the warmth infared radiation of other objects. In other words, to look at the warmth infared radiation of other objects, you need to be cooler than those other objects.
There are not very many options for spacecraft designers when it comes to cooling.
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