## Monday, November 19, 2012

Thinking about the upcoming Macy’s Thanksgiving Day Parade, I thought it might be interesting to consider the physics involved in these floats. With such massive balloons, it must take a lot of physical planning to accommodate the force to make sure that the balloons do not fly away. The parade organizers need to apply an equal and opposite force to the buoyancy force acting on the balloon, otherwise the massive Snoopy, etc. may fly away. So, I’m wondering: how much force is actually needed?

We assume that the parade balloons are filled with Helium gas.
To calculate the buoyant force, I know that
The density of air is about 1.161 kg/m3 and the density of Helium gas is 0.164 kg/m3.
The volume of Helium gas in the balloon is about 20,000 ft3 or 566.3 m3.
Therefore, I calculate that the buoyant force of the balloon is about
To keep the balloon from flying into the atmosphere, the parade engineers must supply about 5,500 N of counter force to the balloon. They do so with the many strings attached to the balloon, as seen in the picture.