Slinging.org Forum - Whistling Projectiles

Dawesome21

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Whistling Projectiles
Jul 15^th, 2018 at 11:21pm

Hey all! Not sure if there is an existing thread on this, but I'm wondering all about whistling projectiles -- from history to physics. This YouTube video discusses potential Roman use of whistling balls: https://www.youtube.com/watch?v=7vJBKfQFD8I

Were there other kinds of historical whistling projectiles? How much evidence do we have for whistling projectiles in history? If I understand correctly, Joerg was NOT drilling the hole all the way through the ball -- does this matter? My first guess is that you would actually want to drill the hole all the way through, but my physics intuition is not great. And does round or oblong make a difference (Joerg says no)? Is a potential good idea for a whistling projectile an oblong glandes with a hole straight down the center long axis? What is behind the actual physics of making something whistle? (A lot of questions, sorry).

This all started when I thought it would be cool to make my tennis balls whistle as I threw them. I tried drilling all kinds of holes through a few of them, but they still make no sound when thrown. Would there be any way to make a tennis ball whistle? Does anyone have other cool hacks for whistling projectiles? Extra points if they would still be safe for backyard practice. I have experienced that rocks whistle when thrown because they are unique shapes and oscillate through the air, but obviously I can't justify throwing rocks in my backyard.

It certainly seems like a solid psychological tactic to make sling pellets whistle -- something that small and deadly coming at you that fast -- and the fact that you can't see it in flight but it will be whistling as it comes -- WOW. I would cower and hide behind something for sure.

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NooneOfConsequence

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Re: Whistling Projectiles
Reply #1 - Jul 16^th, 2018 at 12:43am

Ha! That video has come up on several occasions, but it’s a fun video, even if the science is a little questionable. The physics of the whistling glandes is pretty straight forward. The hole is a resonant cavity. There’s a decent overview of tube resonance here:
http://www.physicsclassroom.com/class/sound/Lesson-5/Open-End-Air-Columns

Drilling holes in a hollow tennis ball isn’t the same as a straight tube made of a solid material, but I’ll bet you could still get it to whistle somehow. I’ll have to think about that one

I have a large black rubber Kong ball that whistles, but even if it hits the ground first, it hits my fence like a cannonball because it’s so heavy.

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“My final hour is at hand. We face an enemy more numerous and cunning than the world has yet seen. Remember your training, and do not fear the hordes of Judas. I, without sin, shall cast the first stone. That will be your sign to attack! But you shall not fight this unholy enemy with stones. No! RAZOR GLANDES! Aim for the eyes! May the Lord have mercy, for we shall show none!“ -Jesus the Noodler

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Kick Forum Moderation Offline Posts: 4451 Finland	Re: Whistling Projectiles Reply #2 - Jul 16^th, 2018 at 2:29am I would guess you could get a tennis ball to whistle but you would have to put something like a washer around the hole to make it a clean hole without lots of fibres messing with the air moving over it. That's just a guess, not based on experience but what I would assume would happen.
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Dawesome21

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Re: Whistling Projectiles
Reply #3 - Jul 16^th, 2018 at 6:16pm

NooneOfConsequence wrote on Jul 16^th, 2018 at 12:43am:

Ha! That video has come up on several occasions, but it’s a fun video, even if the science is a little questionable. The physics of the whistling glandes is pretty straight forward. The hole is a resonant cavity. There’s a decent overview of tube resonance here:
http://www.physicsclassroom.com/class/sound/Lesson-5/Open-End-Air-Columns

Drilling holes in a hollow tennis ball isn’t the same as a straight tube made of a solid material, but I’ll bet you could still get it to whistle somehow. I’ll have to think about that one

I have a large black rubber Kong ball that whistles, but even if it hits the ground first, it hits my fence like a cannonball because it’s so heavy.

Yeah, some of his experiments were not nearly as conclusive as he treated them, but it was a fun video.

When you mention the hole in a whistling glandes as a resonant cavity, are we talking about a hole that goes all the way through, or one that stops a certain distance in? I think the link seems to focus more on "open-end air columns," that is, holes that go all the way through, and this seems to make more sense to me, but I also think Joerg mentioned not drilling his holes all the way through.

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Dawesome21

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Re: Whistling Projectiles
Reply #4 - Jul 16^th, 2018 at 6:17pm

Kick wrote on Jul 16^th, 2018 at 2:29am:

I would guess you could get a tennis ball to whistle but you would have to put something like a washer around the hole to make it a clean hole without lots of fibres messing with the air moving over it. That's just a guess, not based on experience but what I would assume would happen.

That's an interesting idea -- maybe I will try putting a tube through the hole in the tennis ball. I may be able to find a small piece of pvc or make something up with duct tape.

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Kick Forum Moderation Offline Posts: 4451 Finland	Re: Whistling Projectiles Reply #5 - Jul 17^th, 2018 at 1:51am I'm pretty sure the ones found at the site and the ones Joerg made only went in about 2cm. All the examples I've seen haven't been all the way through. Doesn't mean that wouldn't work though.
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NooneOfConsequence

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Re: Whistling Projectiles
Reply #6 - Jul 17^th, 2018 at 8:11pm

The physics are about the same for open or closed tubes. They just give you slightly different vibration modes.

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“My final hour is at hand. We face an enemy more numerous and cunning than the world has yet seen. Remember your training, and do not fear the hordes of Judas. I, without sin, shall cast the first stone. That will be your sign to attack! But you shall not fight this unholy enemy with stones. No! RAZOR GLANDES! Aim for the eyes! May the Lord have mercy, for we shall show none!“ -Jesus the Noodler

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BAMBULA Descens Offline Slinging Rocks! Posts: 153 Russia Gender:	Re: Whistling Projectiles Reply #7 - Jul 17^th, 2018 at 8:21pm https://www.youtube.com/watch?v=sazRtbKiTII https://www.youtube.com/watch?v=svdL-kszLaw
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Dawesome21 Junior Member Offline Slinging Rocks! Posts: 66 Gender:	Re: Whistling Projectiles Reply #8 - Jul 19^th, 2018 at 12:29am Cool YouTube videos -- thanks Bambula. I should try drilling holes in golf balls as well as the tennis balls. I will get around to some more experimentation next week sometime and let you all know if I can get something to whistle.
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BAMBULA Descens Offline Slinging Rocks! Posts: 153 Russia Gender:	Re: Whistling Projectiles Reply #9 - Jul 19^th, 2018 at 4:34am https://www.youtube.com/watch?v=nvoxY0ygw_M Holes of different diameter.
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Dawesome21 Junior Member Offline Slinging Rocks! Posts: 66 Gender:	Re: Whistling Projectiles Reply #10 - Jul 21^st, 2018 at 6:36pm I just rediscovered this old thread: http://slinging.org/forum/YaBB.pl?num=1301002394 I might try to revive things further over there.
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