How To: Vortex Ring Launcher

"SMALL SMOKE-RING CANNONS
Many years ago WHAM-O sold a plastic air-puff gun. The puffs of air could fly across a room and knock over cardboard targets.

It turns out that this gun used ring-vortices, or "invisible smoke rings" as its ammunition. Also turns out that smoke-ring guns are extremely easy to make. Take a soup can, cut out the top and bottom, tape a piece of cardboard over one end, and cut a 1" hole in the center of the cardboard. Tape a disk of thin card stock or heavy paper over the other end (or better yet, snip a balloon in half and stretch it across the other end.)

When you gently whack the covered end of your vortex launcher, a transparent ring of spinning air will shoot out of the hole. Aim the device at your face or arm, and you'll feel the puff of air when it hits your skin.

The vortex rings can be made visible with a bit of smoke. I use stick incense, and just shove the end of the stick into the hole for awhile (don't set the cardboard on fire!!)

Tap the bottom gently, and slowly spinning smoke rings will be launched. Tap it hard, and the smoke rings will zoom so fast that you'll only see a grey blur. Tap it too hard and you generate air turbulence but no smoke rings.

To see the details of the smoke rings it helps to have bright lights and a dark background. Work in a darkened room while placing your device between you and a bright table lamp. The light should shine towards you, through the smoke, but position things so you observe the smoke against a darkened wall. Smoke rings are similar to tornadoes, but the ends of the tornado is curved around so its ends are joined into a circle.

Try shooting slow rings then immediately shoot faster ones. The faster ones will catch up to the slower ones and move through them (the slower ones open wider to allow the fast ones to pass.)

Rather than using smoke, you could instead use scent. Any fumes in the can will end up inside the air in the smoke ring. Try putting perfume in the can. When you launch your ring vortices, they will be invisible. But if you target a distant nose, your victim will know when they've been hit.

Or even easier than building the soup-can launcher, K. Larsen suggests using a 1-gallon polyethelene milk jug. Whack the bottom and a vortex ring is launched from the spout. Aim it at your face and you can feel the rings of air hitting you, even if you don't use smoke."
Article origin http://www.amasci.com/amateur/vortgen.html