Simulations are combined with laboratory measurements to show the important role of shock waves in a popular physics demonstration, the “ping pong cannon.” The simulation and measurements confirm a developing shock wave that reflects from the end of the closed tube and approaching ball and the eventual formation of a transient localized pressure build-up near the exit tape barrier. This burst of pressure peaks within a few microseconds of the ball’s arrival, resulting from the combination of near ambient gas density and shock heating to about . Pulsed schlieren images beyond the exit confirm the sequence of internally reflected shock waves and the intense, hot air pressure pulse that explosively removes the exit tape just prior to the ball arrival.
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The acrylic tube used for much of the study was long with an inner diameter of . The balls were typically in diameter with a mass of . The initial pressures were varied from up to as high as . Similar results were obtained for a PVC tube of about inner diameter.
The shock now moves in opposition to the background velocity of gas driven by the earlier “downstream” passage.
The Piezotronics Model 113A21 Dynamic Pressure Sensor is designed for detecting high frequency pressure phenomena and is well-suited for shock tube analysis.