# Is sound affected by gravity at all?

1. Dec 29, 2013

### Heisenberg52

I'm doing some MCAT practice, and one question asks:

A submarine sends a sonar signal in a direction directly downward. It takes 2.3 seconds for the sound wave to travel from the submarine to the ocean bottom and back to the submarine. How high up from the ocean floor is the submarine? (The speed of sound in water is 1489 m/s).

The answer turned out to be about 1700 m, using simple speed x time to give 3400, and then dividing by 2. Why exactly is gravity not a factor in this problem?

2. Dec 29, 2013

### phinds

Why do you think gravity SHOULD be a factor? Do you think water is compressible the way a gas is?

3. Dec 29, 2013

### Heisenberg52

I thought it would be a factor out of habit I guess. So if the medium is a liquid, is the force of gravity negligible?

4. Dec 29, 2013

### SteamKing

Staff Emeritus
Why would gravity be a factor in the speed of the sound wave? After all, sound is a disturbance which propagates through the medium, not an object which is being dropped from a height.

AFAIK, gravity doesn't affect the propagation of sound in gasses, either.

5. Dec 29, 2013

### Heisenberg52

Ok I see. Thank you guys so much!

6. Dec 29, 2013

### phinds

I assumed that he was thinking somewhat along the lines of:

If the gravity of earth were to increase dramatically then the density of the atmosphere at sea level would increase because of the compressibility of gas, and with a denser gas, the speed of sound would increase.

This of course doesn't work under water because water is not compressible in the way a gas is.

7. Dec 30, 2013

### adjacent

We normally find problems involving objects.That's the habit I guess.Here sound is a propagation of water molecules,not an object.

8. Dec 30, 2013

### adjacent

This thread explains how sound is not directly affected by gravity but by the compression of the medium very well

9. Dec 30, 2013

### CWatters

Interesting that in the sea there is depth (around 750m) at which the speed of sound is at a minimum. This causes a wave guide effect that increases the distance that sound travels...

http://en.wikipedia.org/wiki/SOFAR_channel

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