• To show that air has pressure


  • Water glass
  • Pieces of thin flat cardboard


  • Fill the glass to the top with water.
  • Place the cardboard over the glass.
  • Holding cardboard tightly to the glass, carefully turn the glass upside down.
  • Remove your hand from the cardboard.
  • Hold cardboard in place against the glass.
  • Tilt the glass or hold it sideways and the cardboard still remains in place.
water faucet filling a cup with water  full cup of water tipped upside down on a piece of cardboard cup upright with cardboard on top of cup


  • The water will leak out if the cardboard is not held tightly when turning the glass over.
  • The cardboard sticks to the glass as it is turned.


  • Did the water leak Out? Why? (The water leaked out because it was not held tight enough next to the cardboard.)
  • What could you do to keep the cardboard dry longer? (Use thicker cardboard, answers will vary.)
  • Did the cardboard stick when the glass was turned sideways? Why? (Yes, the pressure of the air next to the cardboard caused it to hold tight.)


  • The air pressure kept the water from falling out of the cardboard covered glass.