Vortex Cannon

Introduction

I generally do Big Brother on Saturday afternoons from about 2 to 6 at Patrick’s house near Central Square. Sometimes we go out for a museum (a trip to the Museum of Science is likely next week), or a movie, but this week I didn’t have any ideas. Patrick had previously showed me some YouTube videos of  water balls, and we’ve done “kitchen science” before, so I was looking into that this morning… but it looked like the listed materials would be hard to obtain, and a number of comments claimed that the video was fake. However, in the related videos, I stumbled across this page on vortex cannons, and decided that would make a fun quick activity. Unfortunately, because I’m an idiot, I didn’t take any pictures >.<.

Materials

Due to the supplies at hand, we had to use a slightly different procedure, but the visual effect was pretty impressive.

• One (1) 1-liter plastic bottle, empty and dry
• One (1) tea candle target
• One (1) fog machine
• Matches (or some other candle-lighting device)
• A room with still air

Procedure

We found two techniques worked pretty well, but produced very different results. One, when combined with the fog machine, allowed us to really visualize what was happen, and gave me the opportunity to explain some of the science to Patrick; the other actually put the candle out.

We first tried it without the fog machine, but couldn’t get the candle to blow out; it turned out that our aim was a bit off. The chemical fog stuff (part of an old Halloween setup) allowed us to actually see and aim the smoke rings, and see the vortices forming.

Grabbing the bottle with both hands and squeezing in a quick pulse produces a large, slow-moving smoke ring, with a long-lasting vortex that you can watch stretch as the ring expands. If you squeeze too hard, you just get a turbulent puff; too soft and you get nothing. It takes some trial and error. While these were nifty to look at, they couldn’t put out the candle, even from only a few centimeters away.

I found tapping one side of the bottle with just two fingertips, very firmly, produced a small but fast burst that formed a very fast-moving smoke ring. You could barely tell it was a ring at that speed. They moved fairly straight (as opposed to the slower-moving rings that tended to drift a bit), but were a bit touchy to aim. Once you connected with the candle flame, it went right out, without any guttering as you would see when trying to blow it out manually. We were able to successfully put the candle out at about a meter.

 Conclusion

This was a very fun demonstration, and only took a few minutes to set up. It also requires no cleanup, and you can hypothetically sneak up on your little sister and blow smoke rings at her. Not that I would encourage that sort of sibling mischief…

One thing I needed was a concrete example of why this is important science, and not just a toy demonstration. It’s hard to explain fluid dynamics to a ten year old. Patrick enjoyed it as a project, though.