Back in September, I attended the Ascension Parish Hot Air Balloon Festival in Gonzalez, Louisiana. There was a variety of balloons with bright colors and different themes. I even had the opportunity to ride in a hot air balloon! Now when I say ride I mean the balloon was tethered and I went approximately 50 feet in the air, but it was still amazing.
Besides wondering to myself why there would be a hot air balloon festival in southern Louisiana, I also wondered what was the science behind the hot air balloon. How does shooting a ball of fire into the center of a giant balloon make it rise into the air?
Hot air balloons actually operate on a very simple principle- hot air rises in cooler air. Hot air is able to rise in cooler air because it has less mass per cubic foot of air. However, the amount of mass in one cubic foot of hot air versus cold air is quite small. One cubic foot of cold air weighs about 28 grams, but when the air is heated it weighs 7 grams less. Therefore, each cubic foot of hot air inside the hot air balloon can lift about 7 grams. One cubic foot of air lifting 7 grams is not a lot, but a collective 65,000 cubic feet of air can lift 1,000 pounds which is why hot air balloons have to be massive.
In order for the hot air balloon to keep rising in the sky, the air inside the balloon has to be constantly heated which is done by the burner positioned under the opening into the balloon. Many balloonists use propane to power the flame in the burner because it can be in a compressed liquid form and contained in a lightweight cylinder. The balloons are often made of nylon because it is a lightweight, sturdy fabric and will not melt at high temperatures. The skirt is the part at the base of the balloon which is also made of nylon but coated in fire-resistant material to prevent the balloon for catching fire. The baskets for hot air balloons are often made of wicker because it is a tough material, but is also flexible and lightweight. Since wicker is flexible it helps to absorb the shock of impact upon landing the balloon.
Hot air balloons are a balancing act that work with a knowledge of science. While they may not be the most efficient forms of travel, they continue to amaze people when large colorful balloons rise up into the air.
By Colleen Murphy