Photos from Jolie Perry, News Photography COMM 1316
Hot air rises, and in SPC Physics Professor Kim Bouldin’s lab, so did a roomful of plastic trash bags. They floated up towards the ceiling, one by one, after much classroom discussion about what laws of physics make the process work.
Bouldin says students were using Archimede’s Principle, which says that the buoyant force on an object is the weight of the fluid that the object displaces.
“So, we got the room good and cold to make the air that was to be displaced heavier,” she says. “This type of flight is known as ‘lighter-than-air’ and includes helium balloons, hydrogen or helium vessels (example: zeppelins), and hot air balloons. This principle also applies to submarines, icebergs, and boats.”
Students built their balloon frames out of plastic straws and birthday candles.
“We also had a safety lesson on fire extinguisher use,” Bouldin says, “and we did the whole liftoff part over a table cover to keep the wax off of the floors.”
For lift off to happen, Bouldin says students had to keep the volume of their balloons (SPC trash bags) relatively large to displace the most cold air with the hot air inside the balloon.
“They also had to keep the weight of the actual balloon as light as possible,” she says, “to achieve a buoyant force which was larger than the balloon’s own weight.”
All the teams at least achieved hovering, Bouldin says, even if they didn’t make it all the way to the ceiling.
“My thoughts are we should have added more candles and structured it better probably,” says student Faith Jost, “but it was fun.”
Bouldin reports no one in the lab set off the sprinkler system.
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