Simple Science: Air Pressure Experiments



[Editor's Note: This is the first installment in our newest monthly online column, Simple Science.  We hope that these fun, educational experiements will be a great way to explore science with your kids in your own kitchen.  Have fun & look for more great experiments from science teacher Steve Davala next month!]

Ever hear about “Air pressure?” In this article, you’ll learn a couple of simple experiments that you can perform with materials found right in your kitchen. The main lesson in these experiments is that air wants to travel from high pressure to low pressure.  There is an old saying that “Nature dislikes a vacuum.” Of course this is not the cleaning type of vacuum, but the lack-of-air kind.  But what is “pressure?”

Air pressure is basically the amount of air in a certain area. Like when you fill a balloon or your tires on your bike. If there is little air in the balloon, there is little pressure. If you fill up a balloon it has high pressure in it. If you let go of the balloon, all the air shoots out, spinning the balloon all over the place. The high pressure air inside the balloon moves to the low pressure air outside of it. Remember, high pressure wants to travel from high to low pressure.

Candle in a Plate of Water:

Materials:

  • a plate
  • water
  • a tall glass
  • a lump of clay
  • a few birthday candles
  • matches (get your parent to help you out with this)
  • food coloring.

Procedure:

  1. Pour water onto a plate so that it fills it and add a drop or two of food coloring.
  2. Stick a candle into a ball of clay and place it in the middle of your plate
  3. You are going to put the cup over the top of the lit candle, make a hypothesis/guess about what you think will happen
  4. Light the candle
  5. Put the cup over the candle

You will see the candle slowly extinguish and then the water will creep up into the cup. Pretty amazing! How does it do that? The hot air caused by the candles pushes air out from under the cup (hot air expands and causes bubbles at the bottom). As soon as the candle goes out, the air cools and condenses, but now there is less air in the cup than when it started. This is low pressure. Remember the rule? The outside air (high pressure) wants to push into the cup (low pressure). Have your child experiment with more or less water, or more candles.

There are many more ways to experiment with air pressure. Here is another quick one:

The Floating Water:

Materials:

  • Drinking glass
  • water
  • index card

Procedure:

  1. Fill the glass completely full of water
  2. Put the index card (or other stiff piece of paper) over the top of the glass
  3. Standing over a sink (it needs some practice…) hold the index card to the top of the cup and flip the cup over
  4. Holding the cup, let go of the paper

The water mysteriously stays “floating” in the cup defeating even gravity, only held up by the card. The trick? Air pressure, of course. When you flip the cup over, a low pressure zone is created inside the cup. The outside air (high pressure) wants to push into the cup and keeps the card in the way!

I hope you can enjoy these simple experiments and learn a little bit of air pressure, as well. You’ll hopefully see this in action with plungers, vacuum cleaners, and even the weather! Have more questions about this, or need tips about science fair ideas around this topic (or others), contact me below!

Steve Davala is a middle school science teacher who likes to write. He’s got two kids of his own and subjects them to these science activities as guinea pigs. Follow him on Twitter or on www.stevedavala.com or email him at steve.davala@gmail.com.
 

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