How to Make Giant Smoke Rings
A giant smoke rings reveals the path of a vortex of air shot from a garbage can.
Toy manufacturers sold small air blasters that sent vortexes of air sailing across a room that surprised innocent victims and delighted not-so-innocent spectators. With a little practice, it was easy to shoot a plastic cup off of someone’s head or ruin 20 minutes of hair brushing from across the room. It was a blast – literally! The Spangler motto: “Make It Big, Do It Right, Give It Class!” resulted in the creation of the Trash Can Smoke Ring Launcher.
- Large plastic bucket or trash can
- Bungee cord (5 ft, 1.5 m )
- Plastic shower curtain or thick plastic sheet
- Utility knife or keyhole saw
- Adult supervision
Turn the garbage can over and use a utility knife to cut about an 8″ (20 cm) hole in the center of the bottom of the can. The cut doesn’t need to be perfect but the more centered and circular the hole is, the better your smoke rings will be. You could smooth and round it with a little sandpaper.
(The smaller version of the air blaster uses a 5 gal (19 l) plastic bucket. Cut a 2- to 3-inch (5-8 cm) hole in the center of the bottom of the bucket. Use care when cutting the hole with a knife or keyhole saw. Adjust the shower curtain and bungee cord as needed.)
A piece of plastic shower curtain works great as the membrane needed. It’s durable and flexible and can be easily trimmed with scissors or a utility knife. Shape it into a circle that hangs over the edge of the can about 10″ (25 cm) all the way around. Secure it in place with a bungee-type cord. The plastic should be snug.
Point the hole in the bottom away from you and sharply hit the shower curtain with your hand or the end of a stick. An invisible blast of air shoots out of the hole. Aim the hole at someone or something across the room and send a blast of air their way with a whack of the plastic membrane. Smile and look innocent when they glare at you.
To share the fun, hold the hole over a smoke source (a smoke generator or a smoke bomb) and fill the container with smoke. Point the hole away from everyone and tap in the center of the plastic to generate huge, rolling smoke rings.
How Does It Work
The correct name for the air cannon, smoke-ring device is “vortex generator”. The “ring” of air that shoots out of the cannon is actually a flat, vertical section of of air. The outer edge of this moving air is rolling backwards on itself. This vortex of air is generated because the air leaving at the center of the hole is traveling faster than the air leaving around the edge of the hole. The air around the edges takes longer to get out of the can. That swirling or vortex motion can be observed if a little smoke is in the container before giving the plastic a tap. This activity demonstrates that air occupies space and the rolling smoke rings are an added bonus.
Bernoulli’s principle states that the faster air is moving, the lower its pressure. Since the air inside the vortex is moving faster than the air outside the vortex, the higher inward pressure from the outside air is the force that holds the smoke ring together. Eventually, friction steals away all the energy stored in the vortex and the smoke ring drifts to a stop and vanishes. Very cool!
Take It Further
You can take this lab further by identifying a variable, or something that changes, in this experiment. Let’s take a look at some of the variable options that might work:
- You can change the size and speed of the rings by changing the size of the hole.
- What might happen if you use a hole that’s not round?
- What happens to the rings if the sides of the can are not sloped toward the hole?
These are just a few ideas, but you aren’t limited to them! Try coming up with different ideas of variables and give them a try!
Whether you choose a traditional smoke machine or the much more exciting smoke bomb technique, the rule is the same: never blow smoke into a face – either of a person or an animal! Aim the rolling rings of smoke into the air.
Also, do this activity outside or be prepared for the smoke alarms to go off. It’s always interesting to have to explain the smoke rings to the fire marshall who’s standing in your space in full fire fighting gear. Been there, done that, and don’t want to do it again.
When you’re talking science, it’s important to use correct terms and to use them correctly. The plural form of “vortex” is either vortices [vor teh sees] or vortexes. Use the one you prefer.