Swinging fire-- why does it make a sound?

The monster attacks the villagers, one of them brandishes a torch. He is able to drive the beast back and save little Mary Lou Hoo by swinging it to and fro whooosh, whooosh, whooosh

Why does the fire make that sound as it’s swung? The unlit torch alone certainly doesn’t make noise. And “unmoving” fire (eg a campfire) makes crackling noises, but no wooshes. If something burns up very quickly, like a piece of newspaper, it can sometimes go up with a wooshing sound. Is that sound caused by the same thing as the swinging fire sound?

It’s the same sound that a fire makes when it is fanned, blown or otherwise aspirated.

I think the sound comes from the turbulent interaction between the airflow that is increasing the rate of combustion, and the extra, and hotter, gases produced by that increased combustion.

We used to do a party trick round the campfire back in the day - you’d wrap a plastic shopping bag (Pick 'n Pay packets worked best for whatever reason) and then set it alight and hold it up. The plastic would melt and then what looked like globules of burning plastic would begin to fall from the stick, making a “zzzzzzzzzzzzzzzip”-like noise as they did so. We never worked out a proper explanation, but our best guess was that the falling flame was causing a turbulant wake of some kind…

I wonder if it still works - it’s been 10 years & I bet they have changed the plastic…


WAG: When you swing something very fast through the air, it makes a wooshing sound because a vacuum is created behind it, and the air slapping back in to fill that void makes a sound. Fire, which is expanding the air around it via heat, causes a larger vacuum to fill when moved.

Ordinary polythene will do this.

Needless to say, there are a number of hazards involved - the drips of plastic are pretty damn hot and the fumes aren’t nice. Not an indoor experiment, this one.

Heh. We did that with dry cleaning bags almost 40 years ago. Twist them length-wise into a rope, and secure with several rubber bands. Suspend from a wire hanger about four feet over a pan of water. Light the bottom, and zone out of the “zzzzzoooopp zzzzzoooopp zzzzzoooopp” noise as the plastic drips into the water.

We called it a “Whispering Maiden”.

That reminds me of when I would set empty Clorox bottles on fire and “napalm” anthills…

What? They were fire ants. rimshot

I used to do that with nylon rope when I was a kid.

I do firespinning for fun (poi, or chains, mostly), and you would not believe how **loud **the whooshing is when you spin two flaming balls around your ears.

Even when spinning slowly (far more slowly that the speed of sound, so no vacuum like the tip of a whip), the whoosh is loud - and it doesn’t get a whole lot louder when you speed up. In fact, when you’re going really fast, and your flame goes blue instead of yellow/orange, it gets quieter again.

I also hang out around very large bonfires. One of the favorite firetender tricks is to place a hollow log up on its end in the middle of the fire. Once the inside is heated and the bottom has burned away a bit, loud roaring flames start to shoot up and out the top of the “chimney log”. But it only works if air can get in near the bottom.

Playing with a Bunsen burner in chemistry the other day, I noticed a similar phenom - if the air vent is too far open, the flame is loud and yellow. When you have the gas/air combo just right, the flame is blue and quiet. So I think it’s a similar thing with torches and chains and chimney logs - when you force more air, more oxygen, into the combustible area, that makes for loud fire. Swinging a torch or a chain pushes the combustible area into more air.

Sounds like Extreme Teabagging.

I’d forgotten all about that, thanks for the reminder. We used to do the same but it was nearer 50 years ago

We did the same thing with plastic soldiers. We called it “Zip Zips” I have no idea why it made that sound and would love to know why.

Jeeze, guess I’ll have to read quicker before I post.

Gallon milk jugs, too.

Me too (but my staff is much much better than my poi), which is essentially why I asked. Practicing unlit was one thing, but when I first lit up I suddenly had WOOSHing going on all around me. Definitely enhances the experience.

Going to burning man? Don’t think I can make it, but I have a friend going.

Nope, I’m not hard core enough to deal with a preschooler in the desert! (Oh, man, she’s almost 3, and that’s the very first time I’ve called her a preschooler instead of a toddler! sniff.) We’ll be at Sirius Rising and Starwood for sure this year, though. I made her a little set of 7" practice chains. They’re the cutest things ever, but entirely impossible to control 'cause they’re so fast! She’ll stand there and grin and shake them, but she hasn’t made a full circle yet. (Of course, she won’t be lighting up for years and years!)