Does sound travel faster in warm or cold air?
I was asked this by the principal of a school I was visiting during Science Week last year. I gave him the short answer… it travels faster through warm air.
Technically that is correct.. it does travel faster through warm air… the molecules in the warm air are more “excited” and will vibrate more easily. Sound needs vibration in order to work so the sound is carried more easily through the air with the more excited molecules than through air with more “still” molecules (cold air).
A good way to think of it is to imagine a line of dominoes. The air molecules are the dominoes.
Sound makes air molecules around the source vibrate and hit off the next molecule which vibrates and hits of the next (just like the dominoes hitting off each other) and the chain keeps going until the sound reaches your ear… and then the vibrations get carried on to your middle and inner ear until they are changed to electrical pulses that are sent to the brain!
And there was me thinking I was keeping this simple… back to the dominoes… just keep thinking of it like a string of dominoes. Actually that is not quite true…. for the domino model to really mimic the movement of sound you have to arrange the dominoes in concentric circles, not in straight lines. Sound travels outwards from the source in all directions.
So there you have it sound does travel faster in warm air BUT it may appear to travel farther in cold air.
This is how that works…
…if the air close to the ground is colder than the air above it then sound waves travelling upwards will be bent downwards. This is called Refraction. These refracted sound waves can act to amplify the sound to someone standing far away.
13 thoughts on “Does sound travel faster in warm or cold air?”
If sound travels faster in warn (less dense) air than in (denser) cold air, why is it that sound travels faster in water than in air?
Good question John. I would say it is due to the density of water being much greater than the density of air. Whereas with warm or cold air, although the warm air may be less dense, its molecules are moving more so it can transmit vibrations more rapidly through it.
Any suggestions on trying to show this concept for a fifth grade science project? My daughter decided to make this her choice and its due next week! We need a display board and to bring in project or take pictures for board of testing being done at home.
Thanks for any feedback!
Hi and thanks for your question. I am really impressed with your daughters project plans! Off the top of my head I have a couple of suggestions… would she consider making a 3D model to demonstrate? She could have a sound source (like a little bell as in the diagram) and a person at some distance away. She could use a mirror to demonstrate the refraction concept. At a guess she could use a little lazer pen to represent the sound coming from the bell and then she would have to work out how to angle the mirror (or mirrors if required) so that the lazer bounces and is redirected onto the person. This would use something visual to represent something we can’t actually see. (obviously there is a safety element to consider with the lazer pen, always keeping it away from anyone’s eyes).
To demonstrate how heated molecules vibrate more than colder ones (and hence infer that sound can travel faster through the more excited molecules) she could use a glass of hot water and a glass of ice cold water. Add a few drops of food colouring into each and see how the colour spreads out much faster in the hot water than in the cold.
That is just two ideas, it has got me thinking of a few more but I’ll need to test them first. I hope this is of some help, if you want to discuss more just drop me an email at firstname.lastname@example.org and I wish your daughter all the best with her project, it is a great idea!
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Oh it was just great ! It helped me alot !
Thankyou so much for such a beautiful explanation ☺☺☺☺☺☺
Really glad it helped Mariam and thanks for stopping by the blog
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Sound appears to transmit farther, louder, and more clearly in cold air. I’m wondering if humidity might have anything to do with this? When the air is cold, it cannot hold as much moisture, and the moisture drops to the ground as dew or frost. When the air is warm, it can hold more moisture, so humidity may be higher. I’m wondering if more water particles in the air mutes the sound? For example, when you try to speak underwater, the sound is muffled and muted. The more water in the air, the more muted the sound, perhaps? The less water in the air, the farther the sound goes and the clearer the sound is?
hi, this is best crisp and short explanation available on internet
Shrimati Naomi Lavelle u should do your science blogging more often
thanks for the beautiful explanation
Thank you very much 🙂
All I know is that I tried to guess the right answer before reading and I got it wrong 🙁 So much for LC physics 😉
Guessing is better than not answering at all ;0) Although I didn’t feel that way when played a safari quiz game with my son the other night hand I lost!!!