ust Like Real Clouds! Experience Adiabatic Expansion with Alcohol and a Plastic Bottle
I’m Science Trainer Ken Kuwako. Every day is an experiment.
Today, let’s explore a simple experiment about adiabatic expansion. It’s easy enough to try at home, but the science behind it is exactly the same process that creates clouds in the sky. You only need a few everyday items, so give it a try yourself!
What You’ll Need & How to Do It
You only need three things: an empty plastic bottle, a quick spray of rubbing alcohol, and shoe deodorizing spray (Amazon).
First, spray a little rubbing alcohol into the empty bottle. Gently shake the bottle so the inside fills with alcohol vapor. Next, spray in a small amount of deodorizing spray and quickly cap the bottle.
Now you’re ready. Simply squeeze the bottle tightly with your hand.
Check out the video below.
When you suddenly release the bottle after squeezing it, the inside instantly turns white and cloudy. That white mist is actually a tiny cloud forming inside the bottle.
Why Does a Cloud Appear? — The Science of Adiabatic Expansion
Let’s break down what’s happening step by step.
The first important point is filling the bottle with ethanol vapor by shaking the alcohol around inside. At this stage, the ethanol is already floating through the air inside the bottle as a gas.
Next, when you squeeze the bottle, the air inside gets compressed. The compressed air slightly heats up because work is being done on it from the outside. This process is called “adiabatic compression.” As the temperature rises, even more ethanol evaporates into gas form.
Then comes the exciting part: when you suddenly release your hand, the compressed air rapidly expands. At that moment, the air uses its own energy to push outward, causing the temperature to drop very quickly. This is called “adiabatic expansion.”
As the air cools, the ethanol vapor can no longer remain a gas, so it condenses back into tiny liquid droplets. Those countless microscopic droplets scatter light, making the inside of the bottle look white and cloudy—just like a real cloud.
Why Use Alcohol Instead of Water?
You might wonder, “Couldn’t we just use water?” Great question.
The temperature change caused by squeezing a plastic bottle with your hand is actually very small. Ethanol is useful because even a tiny temperature change noticeably changes how much of it evaporates into gas. With water alone, the cloud effect is usually too faint to see clearly.
The deodorizing spray also plays an important role. It contains tiny particles that act as “condensation nuclei,” giving the ethanol droplets something to gather around. This is exactly how real clouds form in the atmosphere: water vapor condenses around microscopic particles such as dust or sea salt floating in the air.
The Clouds in the Sky Form the Same Way
Believe it or not, real clouds in the sky are created by the exact same process happening inside this little plastic bottle.
Near Earth’s surface, sunlight warms the air, causing it to rise upward. Higher in the atmosphere, air pressure becomes lower, so the rising air expands and cools. As it cools, the water vapor in the air condenses into countless tiny droplets—and those droplets become clouds.
Both clouds in the sky and clouds in the bottle are created through the same three-step process: expansion → cooling → condensation.
It’s amazing to think that the same phenomenon happening across the entire sky can be recreated right in the palm of your hand with an ordinary plastic bottle.
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Making the wonders of science fun and accessible! Here you’ll find easy science experiments you can try at home, along with simple explanations and useful tips. Feel free to explore more!
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５月のイチオシ実験！
キーンと冷えるドライアイス！気温が上がってくるこの時期・ドライアイスを使った昇華・凝結・等速度直線運動の実験はいかが？
液体ゼロ！ドライアイスが消えるまでの３時間を科学する（昇華・凝結・等速度直線運動）
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