The mysterious whistling tea strainer
August 22, 2020 7:08 PM Subscribe
Tonight while rinsing out our metal tea strainer under the faucet we discovered that if you hold it under the running water at a certain angle it makes a resonant ringing whistling sound. Example here. Not my video, but it is exactly the same as what happened for us. Can anyone here explain in simple terms the science of why this happens?
The tone being generated is about 1kHz. A single wavelength in air is about 14 inches. You can get efficient tone generation with an item 1/4 of the wavelength, so roughly 3.5 inches in size could do it.
posted by coberh at 11:24 PM on August 22, 2020
posted by coberh at 11:24 PM on August 22, 2020
If your metal strainer is built the same way as the one in the video you linked, then it's a flat, springy, flexible disc over the end of a short tube, and that's pretty much the definition of a drum.
A thing that shape just wants to vibrate and resonate. I'm not at all surprised that there's a way to run water through it that encourages that desire.
The pitch at which it vibrates is going to depend on its effective mass, which will be higher when it's covered in water. I would expect its pitch when bowed by a water stream to be lower than the "tink" it would make if you just tap in in the centre with a spoon.
posted by flabdablet at 1:15 AM on August 23, 2020
A thing that shape just wants to vibrate and resonate. I'm not at all surprised that there's a way to run water through it that encourages that desire.
The pitch at which it vibrates is going to depend on its effective mass, which will be higher when it's covered in water. I would expect its pitch when bowed by a water stream to be lower than the "tink" it would make if you just tap in in the centre with a spoon.
posted by flabdablet at 1:15 AM on August 23, 2020
For what it's worth, I ran across something on YouTube the other day that also just wants to resonate, with effects similarly mysterious to those unfamiliar with the physics of air columns and condensation.
posted by flabdablet at 2:16 AM on August 23, 2020 [2 favorites]
posted by flabdablet at 2:16 AM on August 23, 2020 [2 favorites]
Issac Newton noticed (apocryphal) noticed that a pendulum of a certain length always swung back and forth during the same time period. It could be swinging back and forth a couple of inches over a few seconds, or it could be swinging back and forth many feet over the same few seconds.
It's like swinging on a swing, if you push at the right time, you swing higher and higher, but the time it takes to go from one side to the other remains the same..
Everything will have a Resonance where the energy you apply makes the swing go higher and higher until it collapses.
You can make almost anything do this weird thing if you try hard enough (and have enough power).
It's the same thing that can let someone break a glass by singing at it (matching the frequency so that it swings higher and higher until it breaks). Or being able to hit a note in the shower that makes the walls shake.
Check out this: Street artist playing Hallelujah with crystal glasses and replace the the glasses with your filter and the stream of water with a finger.
When you hit resonance... well, a lot of strange noises will make more sense and you':P have the dread that the right sound could make your head explode into a red mist.
posted by zengargoyle at 7:04 AM on August 23, 2020 [4 favorites]
It's like swinging on a swing, if you push at the right time, you swing higher and higher, but the time it takes to go from one side to the other remains the same..
Everything will have a Resonance where the energy you apply makes the swing go higher and higher until it collapses.
You can make almost anything do this weird thing if you try hard enough (and have enough power).
It's the same thing that can let someone break a glass by singing at it (matching the frequency so that it swings higher and higher until it breaks). Or being able to hit a note in the shower that makes the walls shake.
Check out this: Street artist playing Hallelujah with crystal glasses and replace the the glasses with your filter and the stream of water with a finger.
When you hit resonance... well, a lot of strange noises will make more sense and you':P have the dread that the right sound could make your head explode into a red mist.
posted by zengargoyle at 7:04 AM on August 23, 2020 [4 favorites]
One step back...
We are so tuned in this modern world to think that if it doesn't have a mouth or a speaker it shouldn't project sound.
Sound only exists in your brain. Our ears detect vibrations and signal to our brain not only the presence of vibration, but also the frequency. Although, we can only detect certain frequencies. Most vibrations that occur around us are out of our range and so to our senses don't exist.
A lot of what we do detect are the vibrations that are resonated by objects which project the frequency within our ear's range... Usually a bit slower.
A good old fashioned gurgle is easy to detect like the one I hear from my loose leaf tea strainer.
... Although probably not near as exciting as the whistle you've discovered!
posted by Organic4ever at 10:23 AM on August 26, 2020
We are so tuned in this modern world to think that if it doesn't have a mouth or a speaker it shouldn't project sound.
Sound only exists in your brain. Our ears detect vibrations and signal to our brain not only the presence of vibration, but also the frequency. Although, we can only detect certain frequencies. Most vibrations that occur around us are out of our range and so to our senses don't exist.
A lot of what we do detect are the vibrations that are resonated by objects which project the frequency within our ear's range... Usually a bit slower.
A good old fashioned gurgle is easy to detect like the one I hear from my loose leaf tea strainer.
... Although probably not near as exciting as the whistle you've discovered!
posted by Organic4ever at 10:23 AM on August 26, 2020
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posted by phunniemee at 7:20 PM on August 22, 2020 [1 favorite]