"Who you gonna call? Ghostbusters!"
This vortex cannon is one of my favorite toys to take to science and STEM "Magic Shows" because nobody ever expects the sheer force of air that shoots out of the garbage can! It is one of the easiest science demonstration pieces to make and it has a huge impact.
Supplies
Fog Juice for Fog Machine
How to build a smoke ring garbage cannon with laser sights:
Cut a hole in the end of a garbage can. I cut mine to 6 inches in diameter, but you can experiment with different sizes.
Cut a shower curtain (or any thick plastic sheet) with a minimum of 6 inches of over hang on the outside edge of the top rim of the garbage can.
Secure a ping pong ball or a rock in the center with a rubber band, this will give you something to pull the membrane back with.
Pull the membrane (shower curtain) over the opening and secure in place with duct tape.
Use two large bungie cords to hold the membrane in place. Using bungie cords allows you to quickly and easily change out the membrane if it rips (I've had several tear because people get excited and push too hard).
Laser sight: Place a strong neodymium magnet inside the garbage can and a laser pointer (the battery should have enough metal to allow the magnet to hold it in place, even if your laser pointer is plastic).
Strap: Use rope or webbing ($5 at the hardware store) and secure it in place with a few nuts and bolts.
Smoke rings: Fill the garbage can with fog from a fog machine (or smoke machine) and gently push in the membrane - you will get a perfect smoke ring shooting out the end, as long as the air in the room is calm.
How to build a smoke ring cannon from a bucket (the cheap vortex cannon method):
Cut a hole in the bottom of the bottom of a bucket, about 3 inches in diameter.
Place a garbage bag over the large end opening of the bucket.
Use a bungie cord, tie down, or duct tape to secure the garbage bag over the opening.
Push in the membrane and feel the rush of air come out of the hole in the bottom!
Craig Beals visits the set of Montana This Morning to show Ed McIntosh and Russel Nimitz how to share the science of air pressure and wind from the vortex garbage cannon.
The Science of the Vortex Cannon:
When the membrane (plastic over the top) is pushed in, the volume of the garbage can decreases; this, in turn, causes the pressure inside the can to increase. That air would remain in the can, under higher pressure, but because there is a hole in the bottom, the air can travel out. Because the decrease in volume caused an increase in pressure, the air quickly moves out of the hole - this is the same science that causes wind at the surface of the earth! So, you've just created your own wind cannon!
The science of a smoke ring?
The air at the center of the "hole" in the can will be moving the fastest because the air at the edges will be slowed as it touches the sides of the opening cut in the can (friction). The air on the edges will continue to experience friction, even as it moves away from the can, because it will encounter calm air outside the can. This will slow the air at the edges continually as the burst of air moves forward. The air at the center, however, is pushing the air forward and off to the sides. As it moves to the side, it feels the friction we spoke of earlier and slows. This process continues and the vortex, or smoke ring, continues to move forward.
Now, get out there and bust some ghosts!