JoNova

A science presenter, writer, speaker & former TV host; author of The Skeptic's Handbook (over 200,000 copies distributed & available in 15 languages).


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Suck a water balloon into a bottle

If you are not an adult, find one to help you. Matches are strictly not for kids.

NB: The pdf sample pages from the book Serious Science Party Tricks are an even better explanation of how to do this. They make a great print out.

What you need:

  • A balloon (ordinary party balloon)
  • A wide-mouth bottle (pasta sauce bottles or big juice bottles are great for this, use a glass jar if you can’t find a bottle)
  • A pair of tongs
  • Matches
  • A tissue

What to do:

  • Fill the balloon with water. (Put the balloon onto a tap and fill it until it is slightly bigger than the mouth of the jar or bottle.)
  • Light a half-tissue while holding the tissue with tongs.
  • Stuff the tissue into the bottle and quickly put the water-balloon on top.
  • The balloon should be pushed into the bottle.
  • To get the balloon out, tip the bottle and pull on the knot until it ‘pops’ out!
The water balloon will squeeze into the bottle

Why does it work?

As the tissue burns in the bottle it heats up the air inside. Air always gets bigger when you heat it. So the hot air takes up more room than before. You may see it escaping around the water-balloon and making the water-balloon ‘jump’ and jiggle.

After the flame goes out the air in the bottle will cool and shrink back to its old size. But the water balloon won’t let any more air into the bottle. So the pressure drops inside the bottle. The normal air pressure outside the bottle pushes on the balloon and squeezes it into the bottle.

Notice the water balloon acts as a one-way valve! It lets air out, but won’t let air back in again!
Why doesn’t it work?

Some people are having trouble with this one. Here are the most common mistakes and solutions!

  • Don’t use too much tissue. It will go out (extinguish itself), before you can get it in through the mouth of the bottle.
  • Blow into the bottle between tries. You need new oxygen each time. Once a flame has burnt the oxygen inside the bottle, you won’t get another flame to survive. This is essential. But try not to breath any smoke in, because it’s not healthy. Instead of blowing, use a hair dryer if you can.
  • Maybe your water balloon is just too big? (Or the mouth of your bottle is just too small.)
  • The Egg-in-the-bottle version is the same except you use a hard-boiled egg (peeled) instead of a water balloon. Beware: it’s messier and hard to do more than once!!!
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