Does warmer air have less friction than cooler air?

Question

Does warmer air have less friction than cooler air?

Answer 1

Yes it does. On a very hot summer day, I need much more runway to take off in my little aircraft. The air is less dense, which means that I need more speed to get the lift needed. But since friction, or drag - as we call it in aviation - is also less, flying speed is the same.

Aviators calculate what is called Density Altitude. Aircraft and all instruments are calibrated for the Standard Atmosphere (SA) which is 15 degrees Celsius, the average surface temperature on earth. If one flies at a higher temperature, it is like flying from a higher airfield; the air is less dense. In the pilot's operating handbook, there is a diagram telling how long the take-off distance will be at different Density Altitude, i.e. different temperature and altitude. Note that, as already said, the degree of humidity of the air also plays a role. At SA, a cubic meter of air can't contain more than 14 grams water. As temperature increases, it can contain much more. This, incidentally, is the problem with global warming: if the average temperature increases on earth, much more moisture will be sustained in the atmosphere. We still don't know what it will mean for the climate but it will certainly have an effect.

Answer 2

yep

Answer 3

yes,



the molecules are spaced further apart.

Air is a gas, gas expands when it gets warmer.

Answer 4

Air friction depends on speed and air density.  Since warmer air is most often thinner, then yes, it does have less friction.  But it also depends on how humid it is, and the altitude.

But ...comparing air at 32 F to air at 85 F, the difference is only about 10% in temperature.

Answer 5

Yes, because cooler air have it own mass so it have more friction compare with hot air, you can feel it when in summer season and winter season.