The arrival of a full set of photogate timers1 to our high school classroom has enabled a rewarding variety of mechanics experiments. The initial use of photogates, however, presents a vocabulary challenge to students. What do “gate mode” and “pulse mode” mean? I've devised a simple motivating experiment appropriate to early mechanics study to demonstrate these terms. The purpose of the experiment is to find the speed of a flicking finger. Just how fast can a finger be flicked (wrist snap allowed)? Can a fingertip momentarily move as fast as a walker at 1 or 2 m/s? How about a sprinter at 8 m/s? Or perhaps a fastball at 40 m/s? Or greater? By the end of the experiment, students know, and they've used both gate mode and pulse mode to find the answer.

1.
We're using PASCO models ME-9215A, ME-9204B, and ME-8930, and Vernier's LabPro, but other manufacturers offer functionally similar products.
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