Who’s Crushing It? The Scientific Mystery of Why Plastic Bottles Go “Crunch!” (Atmospheric Pressure)
I’m Ken Kuwako, a Science Trainer. Every day is an experiment.
Imagine sitting in a quiet room with no one around when, suddenly, a plastic bottle on the table makes a loud “CRUNCH!” and collapses in on itself… Have you ever seen something that looks as though an invisible giant had grabbed the bottle and squeezed it?
At first glance, it looks almost like a supernatural phenomenon. But this is actually a dramatic demonstration of the “power of air” that is constantly surrounding us. In this experiment, I’ll show you how to experience the incredible force of atmospheric pressure using nothing more than a few everyday items you probably already have at home.
“Who crushed it?” The mysterious experiment where a plastic bottle collapses
Everything you need for this experiment is probably already sitting somewhere in your home.
【What you need】 ・A plastic bottle (500 mL to 1 L is recommended) ・Hot water (use water that has just come to a boil)
【How to do the experiment】
1. Start with an empty plastic bottle.
2. Pour a small amount of very hot, freshly boiled water into the bottle. (Just enough to cover the bottom is fine. Be extremely careful to avoid burns, and have an adult carry out this step.)
3. Put the cap on the bottle and gently shake it. Then immediately remove the cap and pour out the hot water.
4. As soon as you have emptied the bottle, quickly screw the cap back on tightly.
5. Place the bottle on a table and watch it for a while.
And then comes the magic! You can actually watch the plastic bottle suddenly collapse, even though nobody is touching it.
And then, suddenly… CRUNCH!
So who—or what—is crushing the bottle? After a little while, you should see it begin to cave inward with a series of “CRUNCH! CRUNCH!” sounds. It looks just as if an invisible hand were squeezing it. Kids are sure to stare in amazement!
The science revealed! The culprit behind this “mystery” is atmospheric pressure!
The culprit behind this strange phenomenon is none other than “atmospheric pressure.” So what exactly is going on? Let’s break it down into three simple steps.
1. Hot water drives the air out of the bottle
When you pour in hot water, the air inside the bottle is heated, expands, and escapes. On top of that, some of the hot water turns into water vapor, filling the inside of the bottle with steam.
2. Closing the cap causes the pressure inside the bottle to drop
Once the cap is closed, the water vapor inside the bottle cools down and turns back into liquid water. When a gas changes into a liquid, its volume becomes dramatically smaller—about 1/1700 as large! As a result, the air pressure inside the bottle drops rapidly. This is known as a “change of state.”
3. The bottle collapses under the pressure from outside
All around us, there is a tremendous force caused by the weight of the air: atmospheric pressure. The pressure outside the bottle remains strong, while the pressure inside has dropped. The bottle can no longer withstand the pressure from outside, so it gets crushed inward.
Incredible power! Atmospheric pressure can even crush a metal drum
One famous large-scale experiment that I’ve always wanted to try myself is using atmospheric pressure to crush a metal drum.
In this video, the experiment is performed right in front of elementary school students. The sturdy metal drum stubbornly refuses to collapse, and it’s hilarious to watch the children anxiously waiting and wondering, “When is it going to happen? When?!” Their frantic efforts to pour water over the drum to cool it down and lower the pressure are a perfect example of “science in action.”
This phenomenon is based on exactly the opposite principle from what happens to a bag of snacks that puffs up when you take it high into the mountains. Atmospheric pressure, pressure itself, thermal motion, changes of state… A single plastic bottle packs an amazing amount of important science into one simple experiment. I hope you’ll use this spectacular demonstration as a starting point for exploring the fascinating world of science together with your children!
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Let’s bring the wonder and excitement of science closer to everyday life! Here you’ll find fun science experiments you can do at home, along with easy-to-understand explanations and useful tips. Feel free to explore the site and search for more experiments!
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