“Visible Air Cannon” with Dry Ice! Make it with a Milk Carton! ~Smoke Rings Dancing Through the Room~
【This article is also available on the radio!】
When you hear the term “air cannon,” you might just think, “it’s something that shoots out air…” But when the movement of air actually becomes visible, it’s a truly amazing and surprising phenomenon. This time, I’d like to introduce a lesson idea for an “air cannon using dry ice,” which is perfect for visualizing air flow.
This is a very simple yet highly engaging teaching material for students, using familiar materials like a milk carton and dry ice to create smoke rings that appear like a ninja’s trick. Students’ curiosity for physics is naturally sparked, leading them to ask questions like, “Why does it form a ring?” and “Why does it fly?” The setup is easy, and it can be done in a science lab or a regular classroom.
◆ Why is it a “visible” air cannon?
Cardboard air cannons are well-known, but since the movement of air is “invisible,” you can only understand it through visible reactions (like a paper cup being knocked over). By using dry ice smoke, you can visualize the air flow itself. This “visualization” allows you to observe how the vortex ring (a lump of air) flies and disappears, which deepens understanding significantly.
◆ Lesson Preparation and Experiment Procedure
【Materials Needed】
• Milk carton (1-liter size is recommended)
• Dry ice (under 1000 yen for 1kg, available at ice shops and some supermarkets)
• A fish tank or a clear case (approx. 20-30cm deep)
• Hot water (approx. 40℃)
• A utility knife, scissors
• Work gloves or tongs (for handling dry ice)
【Pre-preparation】
• Use dry ice as soon as possible after purchase.
• Some ice shops may require a reservation. Inquire in advance.
【How to Make and Experiment Procedure】
① Processing the milk carton
→ Cut off the top part, and make a round hole of about 4-5cm in diameter on the bottom.
② Prepare the smoke generator
→ Put hot water of about 40℃ in the fish tank, and add a small amount of dry ice.
→ A white cloud of smoke (a mixture of vaporized carbon dioxide and water vapor) will billow out.
③ Place the milk carton
→ Place the carton over the fish tank with the cut opening facing down and the hole facing up, so that smoke fills the inside.
④ Fire the air cannon!
→ Gently tap the side of the carton, and a ring of smoke will fly out!
• The biggest advantage is that students can understand the principle of the air cannon (a lump of air moving forward through a hole) as a “visible phenomenon.”
• Encourage them to observe the shape, size, and flight distance of the smoke rings.
• The question, “Why does it form a ring?” naturally leads to a deeper inquiry into the structure of vortices and the properties of fluids.
• This experiment can be extended to more inquiry-based activities, such as having groups compete to create the most stable ring.
◆ Examples of Expansion and Application
• Advanced questions: “Why does the ring disappear mid-flight?” “What factors affect the flight distance?”
• Comparative experiments: What happens if you use a square hole instead of a round one? What if you change the size of the hole? What if you use a different type of smoke?
• Connections to everyday life: Link the experiment to volcanic smoke, cigarette smoke, contrails, and smoke machines.
Air is “invisible,” but it has power. This experiment, which allows you to visualize that power, is extremely effective for students who struggle with physics. The beautiful and mysterious rings of smoke floating in the classroom instantly convey the wonder of science.
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