Day 61 – Direct Measurement Videos

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Physics 11 – In preparation for the paradigm lab for unbalanced forces, today’s physics classes used Direct Measurement Videos (DMV) to analyze constant acceleration motion of a toy car.

The DMV we used were from Peter Bohacek at Carleton.  They are, simply put, brilliant.  Peter started making these videos a few years ago and in their most basic form, DMV are quite simple.  You shoot some video of an object moving and make sure there is some type of ruler in the scene.  Better videos will be shot at higher frame rates with better lighting, better apparatus and setups with very little lens distortion or perspective.  Once you have a video, you can analyze time (counting frames) and position.

Peter’s newest videos are put into an html5 video player with many more features.  For today’s class the DMV player we used allowed the user to pick different toy cars to analyze.

It took the whole class for students to get used to the software and gather data for analysis.  They were asked to find the acceleration of the toy car, but lots of students started collecting massive amounts of data and plotted position vs time graphs.  This was after we had a class discussion on how acceleration can be calculated directly from d = vot + 1/2at^2, or a = dv/dt, once you find the beginning and final velocity.  I’m not sure I’ll ever quite understand how students get off track so often (well, I think I know why, I just don’t know if I’ll ever get good enough to mostly eliminate it).

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