[Science Supervision] Why Does It Spray Everywhere? The Science Behind Spill-Free Gong Cha Drinks | ZIP (Nippon TV)

I’m Ken Kuwako, Science Trainer. Every day is an experiment.

You grab the cup, jab in the straw, and whoosh! Your drink shoots right up at your face. Ever had that happen? The culprit behind this “overflow incident” is the little bit of air still trapped inside the cup.

On Wednesday, 11/4, I served as the science advisor for “Irritation Relief Files: 6 in a Row – The Gong cha Drink No-Overflow Trick,” a segment on ZIP! (Nippon TV). I’ve appeared on ZIP! once before.

That Annoying Moment When the Straw Makes Your Drink Spurt Out

Sealed-cup drinks like the ones sold at Gong cha come with a wide straw that you stab through the aluminum film on top. Has your drink ever overflowed or squirted out when you did that?

The Trick: Don’t Hold It, Go Straight Down, and Be Quick

Here’s a trick that works: set the cup down on the table and, without holding it, push the straw straight down from above. But why does that stop the drink from spurting out? That’s exactly what I explained as the science advisor on ZIP!

The Culprit: That Little Pocket of Air in the Cup

It all comes down to the small amount of air inside. When you squeeze the cup, the liquid barely compresses, but the air does, and its pressure goes up. Gases shrink when you push on them, and the pressure rises as the volume drops. This is known as Boyle’s law.

On top of that, if the lid dents as you push in the straw, the air gets crammed into an even tighter space, and the pressure climbs even higher.

So the moment the straw breaks through and connects the inside of the cup to the outside, the air in there is at a higher pressure than the atmosphere around it. That difference shoves your drink up the straw and sends it flying.

So Set It Down and Stab It Quickly

That’s why the trick works. If you don’t squeeze the cup, set it down, and push the straw in quickly, you keep the container and lid from changing shape as much as possible. When the air inside isn’t squashed, its pressure stays about the same as the air outside, so there’s nothing to push the drink out.

In fact, you can see similar phenomena all around you. Take a sealed bag of chips up a high mountain, and it puffs up like a balloon. That’s because the air pressure outside is lower up there, so the air inside the bag expands outward. And if you squeeze a plastic bottle hard and then open the cap, the contents are much more likely to shoot out.

Air may be invisible, but it definitely has pressure. A single cup of bubble tea is all you need to prove it.

Try It Yourself

The next time you have this kind of sealed-cup drink, give it a try in this order:

1. Put the cup on the table (don’t hold it)

2. Point the straw straight down

3. Don’t hesitate. Stab it in quickly and vertically

The key is not to use too much force and not to change the shape of the cup. Try “squeeze and stab” versus “set down and stab” with your friends or family, and you’ll really see the magic of air pressure in action.

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Making science more fun and approachable! This blog collects science experiments you can do at home, along with tips to make them work. Feel free to search around and explore!
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テレビ番組監修・イベント等のお知らせ

• 「ネイチャーティーチャー」（TBS）に出演しました。Tverにて11月3日（火）まで配信中です。

• サタプラ（MBS）にて「日常に潜む！ピンチ脱出法について」のコーナーに出演しました。Tverにて11月7日（土）まで配信中です。

• 11/4（水）ZIP（日本テレビ）のコーナー（7:20分ころ放送予定）にて科学監修を担当しました。ゴンチャのストローの差し方に関するウラザワと科学解説についてです。

• 11月27日（金）　テレビ監修番組放送予定
• 12月26日（土）　ナリカサイエンスアカデミー（教員向け実験講習会）開催

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• 『高校入試 分解問題集 理科』（学研）…難しい問題も小さな問題に分解することで、問題を解くことができます。そんな分解の技術が身につくように深く関わりを持って作りました。
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• 『きめる!共通テスト 物理基礎 改訂版』（学研）…　高校物理の参考書です。イラストを多くしてイメージが持てるように描きました。授業についていけない、物理が苦手、そんな生徒におすすめです。特設サイトはこちら。
  

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