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Toroidal vortex from a bottle

Here's a discovery that's too good to keep to myself...

After careful practice, you can snuff out a candle from as far as two metres (~six feet), just by tapping the side of a plastic bottle. This really impresses people at parties and everybody wants to try it.

A smoke-ring is a spinning, doughnut-shaped mass of air (a "toroidal vortex") spinning in an inside-out kind of way, so the air in the middleof the ring is always being blown forwards. This is the concentrated energy that puts out the candle flame, if you can score a direct hit with the smoke ring. This is the tricky part, because without smoke, you can't SEE the smoke ring...

Start practising from fairly close range. Take careful aim at the candle flame, hold the bottle steady against your chest, and tap the side gently but sharply. Don't try to squeeze out the air. There's no need for the plastic to be deformed any more than a couple of centimetres. You are generating a vortex, not "blowing".

Watch the flame. There is a time-delay before your spinning air-ring reaches it. When you miss, the flame bends towards the vortex. If the flame flickers to the right, you missed to the right. If the flame flickers to the left, you missed to the left. Adjust your aim and keep trying. It's much easier to make the flame flicker as your vortex flies past, than to snuff it out with a direct hit. Don't try to tap the bottle any harder: concentrate on careful aiming. Persevere, because success is so rewarding!

At a range of 1.5 to 2 metres, you need quite a few shots before each hit. But it is surprising how much of the initial energy is still contained in the ring of spinning air, even after travelling that distance. Persevere.

Or aim at somebody's face. They can feel a hit. Or watch their hair. Or aim at tinsel decorations, or at thin curtains, or a fine-leaved house-plant. Or drill a small hole in the bottle and carefully push in a glowing incense-stick to fill the bottle with smoke. (Never set fire to your home without a grown-up helping you.) Aim smoke rings along the beam towards a spotlight, for best visibility.

I don't know why I'd never thought of trying this with a plastic bottle before. It's a classic trick to blow smoke-rings out of a smoke-filled container with a hole at one end, by tapping a flexible "drum-skin" at the opposite end. But a 2-litre plastic bottle is the perfect shape and has flexible sides.

The volcano, mount Etna, blows 200m diameter steam-rings

This cloud-ring was photographed after a lightning strike

Baby dolphins have been observed performing amazing experiments with bubble-rings

And finally, Bill Grundmann was the designer of this masterpiece

Never stop playing!