See How Air Pressure Works! Weather Education Week Experiment #5

Follow along with Meteorologist Steve Sosna as he uses a candle and water to show you how air pressure works -- in both weather and in baseball!

NBCUniversal Media, LLC


  • 1 glass of water
  • Blue food coloring
  • 1 plate or pie tin
  • 1 medium-sized candle (must stand up on its own)
  • 1 small cylindrical glass or vase
  • 1 match or lighter


  1. Pour a glass of room-temperature water. Add blue food coloring to the water and mix.
  2. Pour the now-blue water onto the plate. It should be about one-half-inch deep on the plate.
  3. Place your candle into the middle of the plate. It should stand up on its own.
  4. Light match and light the candle.
  5. Place the cylindrical glass over the lit candle.
  6. Watch the water. It should slowly rise in the glass or may bubble.
  7. Wait for the flame to go out. What happens to the water? It should rapidly rise in the glass, before coming to a stop!

What Happened?

Air pressure moved the water!

When the glass was initially placed over the flame, it created warm air in the glass. The warm air expanded quickly and created higher pressure.

When the flame went out, the air cooled and contracted, creating lower pressure. As a result, the air outside the glass was then higher than inside.

Nature likes to equalize. So, the higher pressure needs to flow into the lower pressure area (under the glass) to create balanced conditions. 

In the process, the water is pushed upon and forced up and into the glass, rising the water inside the glass! Once the pressure in the glass and outside the glass are equal, the water stops rising.

This is why high and low pressure are so important to our weather.

High and low pressure are constantly in a battle to balance out over regions. As a result, we see changes to our weather day to day and week to week.

High pressure is commonly associated with dry and warm conditions, while low pressure moving over a region commonly brings cooler, windier or even stormy weather.

Did you try the experiment? We'd love to see a video! Parents, you can upload a video by clicking here. Make sure to include the names of the participants and your home town.

Or, if you are comfortable doing so, post your video on Instagram or Twitter with #WxEdWeek and tag @nbcphiladelphia.

And check back each day at 10 a.m. and 2 p.m. for new experiments during Weather Education Week @ Home! See all our experiments and coverage here.

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