Why do balloons float?🎈

Welcome to Ask Professor Labcoat where Children’s Museum of Atlanta answers YOUR science questions!

Our friend Liam wants to know why do balloons float?

Kate (Professor Labcoat), our sharp, inquisitive and playful Science Educator, gave this answer:

Balloons float because they are filled with helium!

Balloons can be filled with different types of gas. The air we breathe is made up of lots of different gasses. They are too small to see without a very powerful microscope, but they’re everywhere!

The gasses in Earth’s air are mostly oxygen and nitrogen. These gasses are pretty heavy, so they stay down near the surface of the planet, where we live. 

Other gasses are very light and will float away from the surface. One of these gasses is called helium. There are pockets of helium underneath the surface of the Earth. Humans collect that helium in tanks and use it to fill up balloons!

The helium wants to float up, up, and away from the surface of the Earth — so your helium-filled balloon wants to float up, up and away too!  This is why a balloon that you fill up with your own breath will not float; you are filling the balloon with heavy gas instead of light gas.

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