# Paparazzi Flashes

For last Saturday’s Oscar-themed prom, two of my students wanted to make a cardboard wall of photographers. Essentially, a collection of randomly-firing bulb flashes placed on a piece of cardboard.

After experimenting with the capacitor-driven flash units of couple disposable cameras and recognizing they would be too dangerous, we settled on the use of some high-intensity LEDs we took off a string of holiday lights. We decided to use Arduino as our microcontroller platform. To simplify construction, each LED was wired to one pin, with the grounds soldered together.

In testing, these LEDs were receiving about 4.4 V (rms) from their main supply (220 V), so we figured they could handle the Arduino’s 5 V for a short duration without damage. Three of the LEDs together made a light source too bright to look at directly, and that passed for a flash in the interior setting of the prom. Thus, for 8 “cameras” we needed 24 LEDs, and thus two Arduinos.

A former student, currently studying computer science, wrote up the straightforward Arduino script. We considered drawing a random number (0 to 3) to choose which set of 3 LEDs to light, and another random number (0 to 2000) to determine the delay between flashes, but a constant flash interval of 1 second looked better. Indeed, it looked quite good, and after 2 hours of stripping wire and soldering connections, the students were justifiably proud of their work.

# Whose model?

I think my favourite part of the modeling approach is that students discover, and thus gain ownership of, the core ideas of physics. When they extract a formula from an experiment they conducted themselves, it is more real to them.

For the energy model, I made a point of emphasizing student ownership of the model. I rarely orate, but recall saying, “This is not Newton’s kinetic energy equation. It doesn’t belong to dead white men. This is YOUR formula for kinetic energy.”

As an entrance activity, I asked students to write down THEIR equations for three types of energy, and THE equations for three types of force. The performance difference on this proximate test of model understanding isn’t because of phrasing. Rather, it comes from how we learned: forces were wrapped up in Newton’s laws, while energies were MINE.

I think this is a good way to approach the cultural dimension of physics education. It encourages students to build understandings that reconcile their home and school worldviews, while allowing the empiricism of Western science a chance to perform and earn respect at a personal level. Whose equations are these?

In a class of 14, the students got 36 out of a possible 42 for “their” equations about energy, and only 21 out of 42 for “the” equations about force. After some silly statistics, that gives me p=0.33 on the null hypothesis that this test distinguishes something other than how recently they learned the idea. So, let’s call it an interesting subgroup analysis.