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23 July 2014

Dashboard Monk -- where to find the "spring popper" toy


Remember the 2009 AP Physics B exam problem 1?  It described an experiment in which a "spring in a

small jumping toy" was compressed, allowing the toy to propel itself to a measured height.  Varying the mass of the toy caused the measured height to change.  By appropriate graph linearization, the spring's force constant could be determined.

But where to get such a toy?  Thanks to Drew and Robbie in my Tampa APSI for showing me.  Try googling "Dashboard Monk," or click right on the link.  I've seen these toys with Easter Bunnies, pastel eggs, and other themes.  But I've never found them other than serendipitously in dollar stores.  Now you (and I) know how to order these online.

Once you have a class set of these $5 toys, you can do the experiment posed in the 2009 exam.  To vary the mass, stick some putty on the top of the toy; or, wrap some solder around the base.  How do you measure the height to which the toy rises?  Well, that was the last part of the 2009 problem!  Many ways are possible.  I think I will pose just this question one day to a class, saying "determine the maximum height of this toy with nothing other than a stopwatch."  

When you actually do the full experiment, you could certainly use additional equipment to determine the maximum height.  Procedures suggested by students on the AP exam itself frequently referred to video analysis -- put a meter stick in the background and go frame-by-frame near the top.  A fellow reader joked that a student could put his forehead above the toy and see if he got bopped, moving his head progressively higher until the toy merely brushed his eyebrows.*

* No idea whether that's an apocryphal or an authentic answer.

One of the best parts of physics teaching is going to toy stores with the science department credit card in hand.  Thanks Robby and Drew for showing me where to shop.

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