Why does sound travel faster in warm air?

Question

Physics topic

Answer 1

The main idea is that sound is pressure waves. These waves bounce off of the molecules in the air, in a solid, or in a liquid before they reach us.

Temperature is a measure of how fast the molecules are bumping into each other... the higher the temp, the more they are bumping into each other, and the more information they carry when they do hit each other.

Since they are already bumping into each other at a fast rate due to the high temperature, a pressure wave coming along will travel faster.

If it were cooler outside, the molecules wouldn't bump as often, and it would take longer for the pressure wave to travel.

Answer 2

I would venture to guess that sound travels faster in cold air, I could be wrong, here.

Denser materials tend to transmit vibrations faster than materials which are less dense. Cold air is denser than warm air, thus sound should travel faster in colder air.

Honestly, though, the difference should only me marginal.

Now, something very interesting happens if you use hot air that is also humid. Humid air is more dense than dry air and warm air has a better propensity for storing water. It could be argued that humid air transmits sound faster than dry air at the same temperature.

Answer 3

The faster moving molecules of warm air are better at transmitting sound waves. Cold slows the molecules down.

Of course, as long as the pressure is the same in both cold and warm masses.

Answer 4

The traveling of sound depends on the forces between the atoms or
molecules of the medium, and in a gas those force only act during the short
period when they collide. But in liquids and solids the fundamental question
is how fast the atoms jiggle around in their local positions (sound waves are
actually coordinated long-wavelength "jiggles") which gets faster the higher
the strength of the local forces keeping the atoms roughly in place. So,
sound travels fastest in the most strongly bonded materials.

Answer 5

The speed of sound in an ideal gas is equal to the RMS speed of the molecules, and this increases with temperature (the kinetic energy per degree of freedom of each molecule is 1/2 kT).

You can show this from the equation for the speed of sound in a gas v = sqrt (gamma P/rho) where P is pressure and rho is density (ie speed increases as density decreases). Gamma is the adiabatic constant.

You can also express the speed of sound as sqrt(gamm RT/m) where m is the mass of each molecule.

Ignore all answers that say speed increases with density. They don't know any physics.

Answer 6

It doesn't. Sound travels faster in more dense material. It travels faster in cold air. It travels faster in steel. More dense materials have molecules closer to each other. They don't need to travel as far to bump into the next molecule.

Answer 7

Warm air is less dense, so the sound can travel faster.

Answer 8

The molecules are not packed as densely which makes for an easier vibration of the air.

Answer 9

Because it can't find a coat that fits.