Gas station without pumps

2011 November 30

Vernier Video Physics for the iPad 2

I have recently blogged about Tracker for analyzing videos of physics lab experiments.  I like this approach to low-resolution measurement in classes, because it provides much better data than most hand measurements at much tighter time intervals, with much less effort.  I liked it so much that I even spent a week improving the velocity and acceleration computations done by Tracker. It certainly beats the ticker tape and buzzer-with-carbon-paper approach we used in the physics class I took back in 1969–70.

Incidentally, such devices are still made and sold, see, for example. A slightly more modern update uses a periodic spark, see, for example. Some people even use motors with eccentric weights to get sort-of periodic marks on ticker tape (see, for example).

Although I’m fairly pleased with Tracker, I recently found out about an iPad app that may appeal to those already have an iPad2.  Reviewed in Jacobs Physics: Vernier Video Physics for the iPad 2: A Winner, the Vernier Video Physics app looks like it might be handy in a physics classroom.  Greg Jacobs was particularly pleased that the filming could be done with the same hardware and app as the analysis, so that a lot less data transfer and context switching was needed. I can see how that could be a real advantage in the tight time constraints of a short class period. I’m afraid I can’t review the app myself, as I don’t have an iPad2, and I have no intention of buying one in the next year or so.

If I do get something to improve video physics in the next year, it would probably be a high-speed camera, probably a cheap one like the Casio Exilim ZR100 for $250. The resolution vs. frame rate tradeoff is pretty stark—they have a 4000×3000 sensor for still photos, and at video speeds they get:
• FHD : 1920 x 1080 (30fps)
• STD:640 x 480 (30fps)
• HS : 224 x 64(1000fps) / 224 x 160(480fps) / 432 x 320(240fps) / 432 x 320(30-240fps)

64 pixels is pretty low resolution for tracking. It looks like they max out at 76,800 rows per second, which can be 160 rows at 480 fps or 320 rows at 240 fps. Still, either one is twice what I can get with my camera (1080 rows at 30 fps—it is 1080i, though, which means I could treat it as 540 rows at 60fps, if the software treats the odd and even half images separately). The 240 fps shooting looks like it still would have enough resolution to be quite usable, and there are certainly times when trading off a little resolution in space for better resolution in time would be well worth it

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