LIGHTER THAN AIR The Amazing Story of Helium

DID YOU EVER hold a helium balloon on a string and feel it tug toward the sky? Have you ever let go and watched the balloon fly away, growing smaller and smaller until it finally disappeared? Why should a helium balloon behave this way?

Helium is lighter than air. While Earth’s gravity pulls on everything, the Earth pulls harder on the air above the balloon than it does on the helium inside. When you let go of the string, gravity pulls this air downward, and the balloon is pushed upward by the sinking air.

You’ve felt the same thing if you’ve tried to hold a hollow plastic ball under water. Gravity pulls harder on the water than on the lighter ball. If you let go,