Hey
Here is my quistion
Can any body tell me whether density of air increases with increase of temperature or decreases with its reise

Like any other gas it decreases, indirectly proportional to the absolute temperature.

I think Labman means pressure is directly proportional to absolute temperature. From the ideal gas law:

Where P = pressure, = density, R= ideal gas constant, and T = temp in Kelvins.

Actually air is not an ideal gas, primarily due to moisture content. The mositure in air can cause a greater increase in pressure with rising temperature than is predicted by the ideal gas law. This is the reason why those who really care about such things prefer to fill their automobile tires with pure nitrogen instead of plain old air - the nitrogen gas holds less moisture than air, and consequently when the tire heats up a nitrogen-filled tire experiences less pressure build-up than an air-filled tire. Nitrogen is commonly used in automobile racing.

I want to amend my previous post - I was thinking about pressure of gas in a closed container, not density. As temp goes up, the pressure goes up, assuming a constant volume of the container and a constant number of moloes of gas in the container (i.e. constant density).

However, if the question is with respect to how air behaves under typical weather conditions, the situation is somewhat different. In general, the density of the atmosphere gets lower when the temperature goes up. For example, on a hot day in the desert the density of the air is significantly less than on a cool day. Thus for airplanes trying to take off from an airport in the desert (Phoenix, for example), when the temperature gets very hot the density of the air may decrease to the point where the lift the wings can generate is significantly lowered, and so the amount of cargo the plane can carry is reduced. Thus the density is roughly inversely proportional to the temp.

Sorry for the confusion.

Quote:

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Originally Posted by rahul_chaubey

hey
here is my quistion
can any body tell me whether density of air increases with increase of temperature or decreases with its reise

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Sir but when relative humidity increses density decreases as it would increses vapour particle(h2o) as instead of nitrogen whose molecular weight is higher than h2o
As you are aware that if temp decreses relative humidity correspondingly inreases clear it