Key concepts
Surface tension
Human body

Has your stomach ever ached so bad you felt as if it was blown up like a balloon—maybe after the big Thanksgiving meal? You may have had a large amount of gas trapped in your stomach and intestines. But where does the gas come from that makes you feel so uncomfortable? And how does it disappear again? In this activity you will blow some bubbles to investigate how a specific compound can help battle those pockets of air.

Everything you eat ends up in your gastrointestinal, or digestive, tract. This includes your stomach, intestines and other organs that break down the food you eat so that it is useful to your body. Some bubbles of gas (which come from many helpful microorganisms that live inside your gastrointestinal tract to help your body digest food) occur naturally in everyone's body. As gas bubbles form, they can get trapped within the food being digested.

Although a little trapped gas in the gastrointestinal tract is normal, stress or foods with lots of starch can result in more gas production—and large amounts of trapped gas bubbles can cause you to notice it. And the gas needs to escape your body somehow. Some compounds are made to help people expel large amounts of trapped gas. One drug that does this is called simethicone, which is an antifoaming agent. Simethicone does not prevent gas from being made. Instead, it helps the body get rid of the gas at a faster rate than normal.

How does simethicone do this? It has to do with a phenomenon called surface tension, which is created because water molecules cling to one another and pull inward at the water's surface. This is why a water droplet has a round shape. Simethicone reduces the surface tension of the formed gas bubbles, which prevents bubble formation. It also helps to combine lots of small bubbles into larger bubbles, which can be expelled more easily. Want to see for yourself? Don't worry, for this activity you'll just test this on bubbles!


  • Two anti-gas chewable tablets containing simethicone
  • Metal spoon
  • Sheet of paper
  • Two plastic cups or glasses
  • Marker
  • Water
  • Liquid dishwashing detergent
  • Two straws


  • Find a work area that can tolerate liquid spills.
  • Label the two cups with your marker. On one cup write “WITH SIMETHICONE”; on the other one write “WITHOUT SIMETHICONE.”
  • Remove two chewable simethicone tablets from their packaging and place them in between a folded sheet of paper. Fold over the edges of the paper on the three open sides.
  • Use the back of the spoon to crush the tablets into a powder.
  • Carefully put all the powder into the cup that you labeled WITH SIMETHICONE.
  • Fill both cups with water until they are about half full.
  • Mix the water solution with simethicone using the metal spoon.


  • Put a clean straw into each cup.
  • Slowly blow through the straw that you put in the cup without simethicone for about 10 seconds. Do you see bubbles form inside of the water? Did bubbles collect on the surface of the water?
  • Next, slowly blow through the straw in the cup with simethicone, again for 10 seconds. What happens in this cup? Do you see bubbles this time?
  • Now, add about five drops of dishwashing detergent into each of both cups. Stir the solutions with the straws. How does the liquid in each cup look now? Do both cups look the same or is there a difference? What happens to the liquid in each cup when stirred?
  • Once you have mixed in the liquid detergent, again slowly blow through the straw into the cup without simethicone for about 10 seconds. Do you see more or fewer bubbles compared with just water without detergent? Are bubbles accumulating on the surface of the water? How many?
  • Repeat the above step but with the cup that contains the simethicone and detergent. What happens this time? Do any bubbles form on the liquid’s surface? Did you expect these results? Can you explain them?
  • Extra: Try out how much simethicone is needed to be effective. Repeat your tests, but instead of two simethicone tablets only add one quarter, one half or one crushed tablet to the water. Do you see the same effects as with two simethicone tablets? Is there a minimum amount of simethicone you need to see less bubble formation?
  • Extra: In your tests, you used water as a liquid. In your stomach, however, you have lots of acid, called gastric acid. Does the simethicone also work in an acidic environment? Repeat the tests, but this time, use an acid such as distilled vinegar (acetic acid) instead of water. How well does simethicone work in this liquid?
  • Extra: Can you find other substances besides simethicone that can reduce the surface tension of your bubbles in water with detergent? Do some research on gas relief and surface tension and try different liquids or compounds that you find in your kitchen. What other substances help reduce bubble formation? Are they more or less effective than simethicone?

Observations and results
You may have noticed that it is pretty hard to make bubbles using only water. In the cup with just water and simethicone you probably also saw no or minimal bubble formation.

If you add soap to water, however, you get lots of bubbles. This is because bubbles need just the right amount of surface tension to form. Plain water has too much, but soap decreases the surface tension of the water so that bubbles can form. If many bubbles are produced at the same time, they form a whole layer of bubbles on the water's surface that rises up inside the cup.

In contrast, when you blew through the straw into the cup with water and simethicone, even with detergent added, no significant bubble formation should have occurred. This is due to the fact that simethicone also decreases surface tension, but by a lot more than soap. If the surface tension of the gas bubbles gets too low, they will collapse which prevents bubble formation. The effect of simethicone increases the more you add to the water. With two simethicone tablets, you probably saw no bubbles form on the water surface at all whereas with only one half of a tablet, bubbles might have been visible.

Pour all the solutions down the sink and clean your work area with a wet paper towel. Wash your hands with water and soap.

More to explore
Observing Bubbles, from Science Learning
Blow the Best Bubbles, from Scientific American
Large Intestine Function, from Science Learning
Science Activity for All Ages!, from Science Buddies

This activity brought to you in partnership with Science Buddies

Science Buddies