You may be surprised to learn that soap bubbles can’t really fly — they float! A bubble and the air trapped inside of it are both very light. In order to float, the bubble hitches a ride on a gas that is slightly denser than the air trapped inside of it: carbon dioxide!

All objects — solids, liquids and gases — are made of molecules. Density refers to how tightly packed the molecules of an object are. If the molecules of an object are very tightly packed, it has a high density. If molecules have more room to move around, the object has a lower density.

Because the air trapped inside a bubble is less dense than the air outside the bubble, it’s up, up and away! The heavier carbon dioxide in the air around the bubble pushes up on the air trapped inside the bubble and off it goes.

This upward force is called “buoyancy.” If you’ve ever watched a helium balloon or blimp go soaring off into the sky, you’ve already seen buoyancy in action!

Helium is a very light gas, which is why helium balloons float better than balloons filled with regular air.


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  1. But a bubble still floats even if you don’t blow it, just waving the wand in the air creates a floating bubble, so basically it’s the surface area and difference in air pressure.

    • Thanks so much for sharing your thoughts about the science behind bubbles, Rollz! We appreciate your comment and are SUPER glad you stopped by Wonderopolis today! :-)

    • What a SUPER Wonder, Dan! We bet you can do some WONDERing of your own about the way the light hits the bubble. We bet reflection has something to do with it, too…

      We’re proud of all the great WONDERing you’ve been doing lately– keep up the great work! :)

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Have you ever wondered…

  • Why do bubbles float?
  • Why do helium balloons float better than balloons filled with regular air?
  • What makes sodas so bubbly?

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Wonder #57- Bubbles Static ImageVimeo Video

Try It Out

Want to see buoyancy right in your own kitchen? This activity will show you the buoyant properties of carbon dioxide in action!

First you will need a few tall, clear, glass containers. Flower bud vases are great, but drinking glasses will work, too.

Fill each container with a different clear, carbonated beverage. We suggest tonic water, soda water, lemon-lime soda and diet lemon-lime soda. Be sure the bottles are fresh and have not gone flat.

Once you pour the beverages into the containers, you will see little bubbles forming and rising to the surface. Say hello to carbon dioxide! But we’re not done yet.

Try dropping a few dry elbow macaroni noodles in one of the containers. What happens? Small bubbles of carbon dioxide attach themselves to the noodles and give them a lift back to the surface.

The noodles haven’t suddenly learned to float, but thanks to buoyancy, they’re back at the top. You can experiment by adding other items such as raisins, dry lentils and dry corn in the other containers.


Still Wondering

Want to learn more? Here are a couple of resources you can explore.

  • Want to make your own bubbles? This video will show you a simple way to make giant bubbles!
  • Eager to learn more about density and buoyancy? Visit Science NetLinks to take your best guess at whether certain items will Sink or Float? in water.


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Today’s gas-powered wonder explored the realm of science. Join us again tomorrow as we learn about the power of passion and the pen. See you then!

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