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Blow them apart experiment

You will need:

 
  • 2 balloons
  • 2 x 20 cm  length strings
  • 1 rod or stick
  • 2 identical stacks of books

Instructions

 
  1. Stack 2 pillars of books, and place the rod across the two stacks.
  2. Blow the balloons up, tie the balloon ends and attach 1 string to each balloon.
  3. Tie the strings to the rod, so that the balloons hang freely from the rod.
  4. Make sure the balloons are the same height.
  5. Blow between the balloons, can you blow them apart? Try using a hairdryer!
  6. Why can't you do it?
Bernoulli balloon experiment

Why does this work?


The mathematician Bernoulli found that moving air has less pressure than air that is still.
In your experiment a low pressure area was created between the balloons when you tried to blow them apart. The faster the air moved between the balloons, the lower the air pressure in that space.
The high pressure surrounding the balloons pushed the balloons together.

The curved surface of the balloon also makes the air travel faster, causing even lower pressure as the air rushes around the edge of the balloon. Curved surfaces are used to create low pressure areas on plane wings and even F1 race cars! Another simple demonstration of this can be done with a funnel and ping pong balls or making vortex smoke rings. Also, check out this engineering article on F1 aerofoil design!
 
Other air pressure based science experiments
 
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