# Relative velocity of sound

Relative velocity of sound.

As I know that speed of sound in medium is property of medium. And independent of source motion but depend on motion of audience or observer and motion of medium. But it is not clear to me. Please explain it.

• Speed of sound in a medium doesn't depend upon the speed of the observer. So what is your question exactly? – udiboy1209 Jul 30 '13 at 14:24
• @udiboy does speed of sound not depend upon motion of medium of propagation or audience. – Rahul kumar walia Jul 30 '13 at 18:56
• It does depend upon the speed of the medium, but not on the speed of the *audience*(observer). – udiboy1209 Jul 31 '13 at 13:32
• @ thats my point that how and why its depends upon the relative velocity of medium and observer. – Rahul kumar walia Aug 3 '13 at 9:11
• If speed of the sound does't depend on the speed of the observer then speed of the sound act something like speed of light. It is constant irrespective of observer. @udiboy – Self-Made Man Aug 3 '13 at 11:34

Have you heard of doppler's effect? Read this http://en.wikipedia.org/wiki/Doppler_effect

• Hi Simar, link only answers are somewhat discouraged; can you perhaps add more details to your answer? – Ali Aug 1 '13 at 6:09
• @simar Doppler effect don't tell anything about velocity of observed sound wave its tell about the observed frequency of wave as function of observer velocity. my ques is how speed of sound related to relative velocity of medium and observwer. – Rahul kumar walia Aug 3 '13 at 9:10

Velocity of sound depends on the velocity of the medium, because in the frame of the medium, the velocity of sound is constant.

It is constant because the velocity can be derived using Newton's laws, and Newton's laws don't change in any inertial frame(constant velocity frame like the frame of the medium). So if you are in the frame of the medium, the velocity of sound will be the same in that frame as what it was in the ground frame.

For eg. If a wind of $400 m/s$ is blowing eastward, and the speed of sound is $300m/s$, the sound waves travelling eastward will have velocity of $700m/s$ eastward, sound waves travelling westward will have a velocity of $100m/s$ eastward, and sound waves travelling northward will have a velocity of $\sqrt{300^2+400^2}=500m/s$ at an angle of $37^o$ to east.

Now if you are in the frame of the observer, the velocity of the medium in that frame will change, hence the velocity of sound will change.

Hope it is clear to you now!