The pressure is on!

Here is a simple trick to play on Dad or Mum...

So you think that you have finished with that 1.5 litre soft drink bottle now that you have guzzled the last drop? Did I hear you say that it's empty? Surely not! It is still full!

Make a bet with Mum or Dad (or your teacher!) in this next demonstration that proves the bottle really is full...

Lets have some fun!

Place an uninflated balloon into an "empty" plastic soft drink bottle with the neck sticking out from the screw cap of the bottle.

  • PREDICT: Ask your students "What will happen when you blow air into the balloon?"
  • OBSERVE: Ask a volunteer to blow up the balloon so it fills the bottle.
  • EXPLAIN: What does this show us? (seniors might like to consider the forces involved
No matter how hard they try, they can't do it!



Air trapped behind the balloon can only be "squashed" or compressed so far and then it "pushes" back preventing the ballon getting any bigger. The pushing of air is called air pressure. When air pushes against something it is called pressure.

Air pressure is all around us as we live under a "sea of air" - a bit like a fish surrounded by a sea of water. The air presses on us from all side, but we are so used to it we don't feel it. Every part of our body is pushing back (each cell is like a balloon) so we don't get squashed flat.

We can see what will happen to a helium filled balloon if it rises too high in the air. The higher up in the sea of air (atmosphere) the balloon goes, the less air pressure there is. The gas in the baloon still pushes outward even though there is very little air pressure push back. The balloon swells and expands due to the greater air pressure inside compared to the outside...until it eventually explodes!

Astronauts have to wear a space suit, not only for air to breath, but to contain air at the correct pressure to push back against their bodies. Find out about sea divers and "the bends".


  1. Find out about living in space. What would you need to take with you for a journey to the Moon?
  2. Want to show that air is heavy? Try this next demonstration!
  3. How is air pressure connected to predicting the weather?
  4. The interactive pages...arrange the planets of our solar system
  5. The interactive pages...uncover the hidden secrets of each planet

RETURN TO FUN! Science Activities and Technology Projects


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