Did You Know: Wind Doesn’t Make a Sound Until it Blows Against an Object?

WIND1This gets into some pretty complex areas of the physiology and physics of sound as well as fluid flow, but the main fact (generalisation) to realise is that fluid that is moving in straight lines doesn’t make any noise. Don’t believe me? Get a garden hose and turn it on. Listen to it, no sound. Now kink the hose a little and you will hear the water running through it quite easily.

Sound as we hear it is caused by pressure waves in the air. In simple terms that means that something has pushed the air in one location, and that push has been shunted form air molecule to air molecule all the way to our ears. Or to put it even more simply, something got the air moving faster and that movement has made it to our ears and been trnaslated into sound.

Now if sound is just caused by air moving then it might seem like wind would have a sound, but it doesn’t. That’s because sound is movement within the air.

We only hear a sound if part of the air moving faster relative to all the rest. It is the change in the speed of the air we respond to, not the speed itself. In contrast wind is a movement of air. With a steady wind there is no change for us to detect. The pressure from a constant wind is, well, constant. With no change in speed we can’t hear wind itself.

As you’ve noticed, we can hear wind if it slams into something like a leaf, that’s because striking the leaf causes the air in that location to slow down. Now we have an area of air that is moving at a different speeed to the rest, and that we can detect as sound.

wind 2We also hear wind whistling in our ears. It’s not the wind flapping your ears, your ears themsleves don’t move. It’s because the air is slamming into the little knobs on the external part of the ear and slowing down. Once again, a change in speed of the air, and we detect that as a sound.

In a parking lot wind won’t make any sound because there is nothing for it to strike, hence nothing to slow it down. The air will flow in nice staright lines and wind speed will remain constant. With no change in speed there is no sound.

© 2012 SAT Telecommunications Ltd.

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