## Sunday, December 3, 2017

### The Physics of the Macy's Thanksgiving Parade Balloons

While home for Thanksgiving break, I watched the Macy's Thanksgiving Parade with my family on TV. It's not that exciting to watch now but I used to love it when I was a kid! However, now that I can see physics everywhere, I was intrigued by how those giant, massive balloons can stay afloat. The big bird balloon weighs 468 pounds (https://www.nyctourist.com/macys_news_parade_balloons.htm). This means its downward gravitational force is around 2,070 N. How is it possible to this to stay high in the sky? Hmm... with some thinking I remembered the buoyancy force that we learned about before break and its application in last week's lab.
In order to float, the buoyant force must be greater than the weight. Here's a diagram:
Source: https://www.quora.com/What-makes-balloons-float

This all happens because there is a pressure difference between the bottom and top of the balloon (P = F/A = ρgh). Although this effect may be appear to be relatively negligible in average balloons, it is heightened when you take into consideration the large size of the Macy's balloons. It is easy to think about this phenomenon: there is a lot more pressure at the bottom of a pool than at the top of a mountain. So, the bottom of the balloon experiences more pressure than the top- pushing the balloon upwards.

This is also why so many people are required to hold the balloon down!

By exerting a downward force on the balloon, the people can compensate for the difference in weight and buoyant force to keep the balloon from floating away.