# Homework Help: Does Sound Effect Temperture?

1. Feb 9, 2009

### Newton V

1. The problem statement, all variables and given/known data
I know what Temperture effect the sound, but does sound effect the temperture? if so in what kind of way?

2. Relevant equations
Not much equation about these yet...

3. The attempt at a solution
Googled it, but everyone saying temperture effect sound...

2. Feb 9, 2009

### Newton V

Need some help with this guys...

3. Feb 9, 2009

### Razzor7

Sound is vibration.

EDIT: Honestly I'm not entirely sure I know the answer, but I'm fairly sure. That hint is the key to my reasoning.

4. Feb 9, 2009

### Newton V

i know, however it might effect temperture, since vibration cause movement and therefore , our air get hotter right?

5. Feb 10, 2009

### Carid

Have you noticed that on a cold night we can hear things much better?
Sound travels throught materials.
If that material is dense the sound travels faster.
Sound in a iron rod will travel faster than sound in water.
Sound in water will travel faster than sound in air.
Now if we heat up the air, the air becomes less dense, so sound travels more slowly in hot air than in cold air.

6. Feb 10, 2009

### cjl

Carid: actually, the speed of sound in a gas goes as the square root of the quantity gamma*R*T. Therefore, as the temperature increases, the speed of sound in air goes up.

7. Feb 10, 2009

### minger

Right, cjl, the speed of sound can also be written as:
$$c = \sqrt{\gamma\frac{p}{\rho}}$$

So, for the original poster. As the temperature increases, the speed of the propagating sound wave will also increase. Can you think of any relations which involve wave speed and other wave properties?

8. Feb 10, 2009

### Carid

cjl

Thank you for the correction.
If I'd thought for a moment I'd have realised this.
On a cold night we can hear things further away due to the refraction of the sound in the air, the air nearer the cold ground travelling slower.

9. Feb 10, 2009

In a sound wave energy is passed from layer to layer but not with perfect efficiency and as with all energy changes the waste energy is converted ultimately to heat.

10. Feb 10, 2009

### Newton V

OMG!!!
I am asking for the effect of sound on temperture not temperture on sound!!!

11. Feb 10, 2009

### Newton V

as it appeared to be, i have to do this alone by myself...

12. Feb 10, 2009

### AEM

Well if you really want to know you could go to the library and take out the book
Theoretical Acoustics by Morse and Ingard. Pages 228 - 230 discuss this in more detail than you want to know. The bottom line: The exact details depend on what the sound is traveling through. Here's a quote: "In fluids with a very large thermal conductivity the temperature is practically unchanged by the passage of the sound wave." The thermal conductivity of air is not especially large and so you can expect that there will be a small change in temperature caused by the sound wave. The exact expression for the change in temperature under adiabatic compression (no heat flow) for an ideal gas is given on page 231 of the text I mentioned.

13. Feb 11, 2009

### Newton V

ok thanks, however what happen in vacuum...

14. Feb 11, 2009