The Desk-Lifting Trick: How Invisible Air Can Lift a Cow (Seriously!)
I’m Ken Kuwako, a Science Trainer, and every day is an experiment!
“Air” surrounds us everywhere. It’s such an obvious, everyday presence that we rarely stop to think about its weight or force. But what if this invisible air held enough power to effortlessly lift a heavy school desk? Today, I’m going to introduce you to an amazing science experiment that lets you feel the incredible, hidden power of air—Atmospheric Pressure—with nothing more than a single plastic sheet!
【This article is also available as a radio broadcast.】
When teaching “pressure” in a science class, the classic experiment of crushing a can using atmospheric pressure is a staple, but it can be a bit tricky to set up. If you want a more straightforward and dramatic way to experience the power of air pressure, this “Lifting a Desk with a Plastic Sheet” experiment is perfect. All you need are three things: a desk (found in any classroom or home), a plastic sheet/binder cover, and a couple of suction cups, both easily available at a dollar store. The setup takes only a moment, but it will simultaneously amaze students with a reaction like “Wait, that’s all it takes?!” and inspire a realization: “Air pressure is that strong!”
This experiment can be done anywhere—in a regular classroom, a science lab, or even your living room at home. Come and enjoy the moment when the force of air truly becomes “visible.”
Experiment Setup and Procedure
◆ Materials Needed (Per Group)
- Plastic Sheet / Binder Cover (B5 size, approx. 18.2 cm x 25.7 cm) … 1
- Suction Cups (approx. 3.6 cm in diameter) … 2
*I purchased both items at a 100-yen shop (Seria).
*I prepared 12 sheets and 24 suction cups for the class, depending on the number of groups.
▼Sample Product Reference:
- “Mini Super Hook, Suction Cup Type (Pack of 5)” ¥110 (Tax Included)
- Similar products are available on Amazon and Rakuten.
◆ Experiment Method
- Wipe the desk surface clean and place the plastic sheet flatly on top, ensuring no gaps are left underneath.
- Firmly press and attach the two suction cups near the center of the sheet.
- Hold the handles of the suction cups with both hands and try to pull straight up, very slowly.
【Key to Success】
The secret to this experiment is to lift the sheet “slowly.” If you pull too quickly and forcefully, air will rush in between the sheet and the desk, and only the suction cups will peel off. By applying force gradually, you’ll experience the strange sensation of the sheet clinging to the desk, causing the entire desk to lift up!
Why Does a Plastic Sheet Lift a Desk?
No, the desk didn’t float by magic! The star of this phenomenon is the weight of the air surrounding the Earth: Atmospheric Pressure. Normally, the air pressure acting on the plastic sheet is equal from above and below, so the forces balance out. However, by placing the sheet flat against the desk, you expel the air trapped between them. As a result, the upward force of the air is virtually eliminated.
This creates a situation where a colossal column of air pressure is pressing down only on the top of the plastic sheet. Because this invisible force is so incredibly strong, the sheet is sealed firmly against the desk. When you try to lift the sheet, the whole desk comes with it!
This is the exact same principle that allows you to drink juice through a straw and that makes suction cups stick stubbornly to a wall. Our everyday world is full of wonders woven by the power of atmospheric pressure.
Science Fact: Let’s Calculate the Force of Air Pressure!
So, just how much force is pressing down on this B5-sized plastic sheet (182mm x 257mm)? Let’s do the math and be astonished by the result.
We’ll assume the standard sea-level atmospheric pressure is about 1000 hPa (Hectopascals). This means a force of approximately 100,000 Newtons (N) is applied per square meter (m²). The calculation is as follows:
F (Force) = P (Pressure) × S (Area)
F=100000Pa×0.182m×0.257m≈4677N
Converting this 4,677 N of force into weight is equivalent to a staggering approximately 467 kg (1,030 lbs)! This is the equivalent weight of three professional sumo wrestlers or a small cow! Can you believe that this immense, incredible force is constantly pressing down on a single plastic sheet? Our own bodies are also continually supported by this same invisible power.
Advanced Learning Ideas
Let’s calculate this surprising force on an even more familiar scale.
- How much air pressure is pushing on your palm (approx. 15 cm x 10 cm)? The calculation reveals a force of about 150 kg (330 lbs)! Essentially, the force of an average adult man is constantly resting on your palm.
- What about your index fingernail (approx. 1 cm²)? It’s about 1 kg (2.2 lbs). Imagine placing a 1-liter milk carton on your fingernail—that’s the force!
It’s also interesting to use educational tools like Narika’s “Gomu Pita-kun” (Rubber Clinger). The sensation of it sticking firmly to a desk allows you to feel the presence of atmospheric pressure even more directly.
Did you feel the force of the air? Knowing the scientific principles hidden in the things we take for granted can make the everyday world look completely different. Please try this thrilling experiment at home or in your classroom!
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