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The Science Behind Parade Balloons


Last Thursday, thousands of people watched as giant balloon characters made their way down the Benjamin Franklin Parkway in the Philadelphia Thanksgiving Day Parade.  Although it’s not a well-known fact, chemistry and physics kept those colossal structures from towering over the on-looking crowds. 

Parade balloons are sealed with nylon and filled with helium.  Nylon is the same nonporous material used to make the inner tubes of bike tires, and helium is used to inflate everything from small party balloons to large blimps. Helium is represented on the Periodic Table of Elements by the symbol He and is the second lightest element.  It takes between 10,000 to 14,000 cubic feet of the stuff to make a parade balloons fly.  With that much helium, parade balloons can soar up to 20 stories high!

So how do parade balloons stay grounded? The answer is, each parade balloon is handled and directed by a well-trained team.  This team consists of a pilot, two co-pilots, a captain, two co-captains, and with dozens of other handlers who offset the upward motion of the helium by pulling down on ropes attached to the balloon.  Without the opposing force of the handlers pulling the balloon down, the balloon would soar right off into the sky (and probably right into a building). Now that would be a sight!

But the physics of opposing forces isn’t the only thing that affects how giant parade balloons work.  There’s another physics principle at work called Charles’ Law.  Named after French natural philosopher Joseph Louis Gay-Lussac, Charles’ Law states that as temperature increases, gas molecules spread out, and gas volume increases.  So, if it’s really hot outside on a parade day, the gas molecules inside the balloon will expand, making the balloon look really full. It may even look like it’s about to burst at its seams.  But if it’s really cold outside on a parade day, the gas molecules inside the balloon will contract, making the balloon look somewhat deflated. 

So with showers of snow, freezing rain, and temperatures dropping around 40ºF last Thursday, Thanksgiving parade-goers might have noticed that the Elmo and Horton looked a little shrunken.  Even so, they still looked cheery and buoyant as they floated above the crowds!