Students in Mr. Dehetre's 6th grade STEAM class are learning about fluids through pneumatic and hydraulic experiments thanks to a grant from the Yarmouth Education Foundation.
Our first experiment dealt with learning the units of measure used for air pressure by using an air compressor to inflate a bicycle tire. The units we studied are PSI (pounds per square inch) and Bar. After using a full size construction type air compressor, students were challenged to build a balloon inflator using the Fischertechnik pneumatics kits funded by YEF. The task was to build the inflator, study the strength of the material the balloon is made of through observation and feel, and then estimate in time how long it would take the inflator to burst the balloon. Students learned that the material was a lot stronger than they initially thought, and that the strength of the compressor wasn't as strong as they thought either. Most balloons took between 12 and 13 minutes to burst. Our experiment was successful as students learned about estimation.
However, a second question surfaced. What causes the balloon to make the "pop" sound? We began to think like scientists.
Students felt that the sound was made by the balloon material snapping back to it's original state. Is that the cause? Could it be the difference between the atmospheric pressure and the inside pressure of the balloon? Thus, when bursting, a small shock wave is produced as the released air moves from high pressure to low pressure and back until it equalizes with the atmospheric pressure. That was Mr. Dehetre's guess as he thought back to his college physics classes. It was just a guess and students were reminded that it was only a guess.
We made a slow motion video of a balloon bursting and broke it down frame by frame. Over vacation, Mr. Dehetre contacted Dr. Mark Semon, professor of physics at Bates College with the question as to what is causing the "pop" noise. After discussing Mr. Dehetre's thoughts with his colleagues it was agreed that his guess was most likely correct. The professor doesn't believe that the balloon material could make the "pop" noise and that it was the difference of air pressure within the balloon equalizing to the atmospheric pressure.
Here is a break down of each frame from our slow motion video. Frame 1. Sam is blowing up the balloon. Frame 2. Balloon seems to be getting thinner on one side. Frame 3. Balloon bursts. Frame 4. Wave of air begins. Notice Sam's hair. Frame 5. Air finally reaches Sam's hair. Frame 6. Second wave seems to begin but doesn't seem strong enough.