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It's raining tennis balls!

by Anthea Ayebaze | Sep 28, 2016

Tennis balls raining from the Chime Tower is a sure sign that school has started on the North Manchester campus. Professor Greg Clark has had his Physics 210 class doing a variation of the experiment for about 15 years. Sitting in the president’s office means I have a front row seat.

I asked Greg for a simple explanation and this is what he sent me: “In a nutshell, students experimentally determine the free-fall acceleration (gravitational field strength) here at MU using their cell phones to take videos of a soccer ball dropped from the tower. They use software to analyze the video and produce graphs of the ball’s velocity vs. time and extract the acceleration.  They then use this and the average time of fall of a bunch of dropped tennis balls to determine the height of the tower using elementary kinematics.”

Got it. Sort of. Actually, not so much.

I thought maybe the lab instructions would help: “Determine the height of the Manchester Chime Tower, h ± δh, by modeling the motion as that of a body undergoing free-fall using your experimental value of g ± δg. Make multiple measurements of the time of fall and use the average time to calculate the height of the tower. Show all of your calculations and assumptions in a logical, easy to follow manner. Use MKS units for the calculations, but give the heights in meters, feet, and yards. Also, determine the speed with which the ball hits the ground.”

Reading the instructions reminded me that I can’t help the students much when they are doing their calculations outside my window. Based on several years of observation, though, I could provide lots of guidance about the best ways to retrieve errant balls that bounce into or under the shrubs around the Administration Building or dodging cars when the balls make their way across College Avenue.

Perhaps most importantly, I can help Greg meet one of his long-term goals: making sure there is safe roof access on the new Chime Tower when it is built.