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Kitchen Science: What Can You Learn From a Cup of Water?

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October 11, 2012

The second in our series of science experiments. These are a great way to explore the world around you – and for some schools an experiment for the science fair is mandatory. At a loss for ideas? Here’s another one to test.

Children are naturally curious creatures and every day we are presented with teachable moments that we may not even realize exist.  Encouraging a child’s natural curiosity will ensure that they grow up wanting to understand how things work and why certain things happen the way they do.  Science does not have to be intimidating and can often be taught using everyday household items instead of a textbook!  Here is a simple science experiment to help explain the forces of gravity and air pressure.


  • Clear cup with a little water
  • Playing card
  • Paper towel to clean up spills


  1. Fill your cup about half full of water. Too much water will result in a mess, so don’t put in too much.
  2. Pour the water from the cup into the sink and observe what happens.  The water pours quickly out of the cup, right?
  3. Now, refill your cup to about half full again. Place the playing card over the cup, covering the top of the cup completely.
  4. Hold the card in place and carefully turn the cup over. Keep your hand on the card for a few moments, then remove your hand.

What Should Happen:

When your finger is removed from the base of the card it will stay in place and continue to hold the water inside the cup.


In the first part of the experiment, the force of GRAVITY pulled the water from the cup into the sink.  Gravity will pull all things towards the earth.  The only way to prevent gravity from pulling something towards the earth is to find another force to act against it.

We are surrounded on all sides by air molecules.  We can’t see them, taste them, or feel them (unless the wind is blowing!) but those air molecules are always there.  The force that keeps the card and water INSIDE the cup is called AIR PRESSURE.  The air below the cup is actually pushing up on the card.   The upward force of air pressure against the card is enough to cancel out the effect of gravity on the water inside the cup.  This allows the water to “float” inside the cup. If you add too much water to the cup, the air pressure won’t be strong enough to cancel out the force of gravity and you will have a mess on your counter!

Take it Further:

Have fun with this!  Encourage your younger children to draw a picture of ‘Captain Gravity and his arch rival Sir Air Pressure’.  Make up a chart with your older child to see exactly how much water is needed in your cup before gravity wins and the water comes falling to the counter.  Make science fun and your children will want to keep learning.

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