All Resources

Incompressible Water

Water is incompressible, which means that you can't squash it to make room for air. Air is compressible, which means that you can compress (or squash) the air and add a little bit more air.

Think of two bottles:

One bottle is entirely full of water – you can't blow air into this bottle.

The other bottle has an air gap at the top. If you add pressurized air, you can actually see the air bubbles going into this bottle. This increases the pressure inside the bottle.

This is a recommended pre-visit activity for a field trip to Science World . It is related to exhibits in the Eureka! Gallery.


  • Investigate the properties of liquids and gases.

  • Describe the relationship between pressure and force.


  • two identical bottles

  • one-holed rubber stoppers or corks that fit tightly in the bottle necks

  • glass, plastic or copper tubing that fits snugly through the hole (copper tubing and a tube cutter can be purchased at a hardware store)

Key Questions

  • Why does the water from the bottle spray you when you pull the straw out?
  • What did you observe during the experiment?
  • What was different between the two bottles?
  • When you blow air into the bottle where does it go? Why?

What To Do

  1. Fill one bottle entirely with water and insert the stopper.
  2. Fill the second bottle with water, leaving 5 or 6 cm of air at the top. The tubing should stick down into the water when you put the stopper in.
  3. Pick two student volunteers and give each one a bottle. They each blow as hard as they can into the straws.
  4. On your signal, the students should suddenly pull the straws out of their mouths and step back.

Teacher Tip: You may want to do this experiment outside so you don’t need to mop up any spilt water!


  • Why can't you force air into a full bottle of water?