Whistle - How does a a whistle produce sound?

[ajayguhan]

whistle -- How does a a whistle produce sound?

How does a a whistle produce sound? And what makes galton or dog whistle to produce high frequencies ...?

 

[Simon Bridge]

That's a great question - what have you done to attempt to answer it?
For instance - have you tried googling the question?
http://en.wikipedia.org/wiki/Whistle
http://www.americanwhistle.com/how.html

 

[ajayguhan]

I read the second link before, it states, "Air enters the whistle at one end. As the air reaches the other, closed end, all the air molecules "pile up" on top of each other and cause a high-pressure region. The air escapes out the little hole in the end, making the noise you hear."
Didn't get it.

Just the escape of air creates noise...? Something I'm missing.,

 

[Simon Bridge]

Exactly - escaping air creates a noise.

Since there is a big pressure difference and a small hole, the air vibrates as it escapes instead of coming out smoothly - and that also vibrates the tube of the whistle. You can make a louder noise with less effort by adding something that helps the air vibrate - like a reed, a thin edge cut into the tube, or a pea.

The frequency of the vibrations depends on the geometry of the tube.

 

[ajayguhan]

We blow the air inside with great velocity that means pressure is lower than the atmosphere so the air outside the whistle must flow in...?

 

[Simon Bridge]

You blow air from your lungs into the whistle - so there is more air inside than outside.
If it was in equilibrium, then the air pressure inside would be higher than outside.
But it is not in equilibrium: there is a hole letting the air out and you cannot keep blowing at a constant rate forever. By blowing you are forcing high pressure air into a chamber and then out through a small hole.
But the pressure is not a constant through the whole whistle.

Maybe you should start with simpler arrangements - you can make a tone just blowing air through your lips ro your teeth right? How does that work?

 

[ajayguhan]

Okay but why do we need a cork inside...?
It increases the intensity or the frequencies of sound ..?

 

[Simon Bridge]

The small ball inside an American whistle (called a "pea") is there ti make the sound warble a bit - it does this by randomly interrupting the airflow as it bounces around. Not all whistles use them. The rapidly fluctuating tone attracts attention easier than a uniform tone because of the way human biology/psychology works.
See the second link post #2.

 

[ajayguhan]

Thanks, i understood now ...!