Feb 8, 2014

YouTube Frame by Frame

I've been looking for a while for a way to watch YouTube videos frame by frame - to encourage rough quantitative analysis of videos directly online without loading them into a video analysis program like Logger Pro. I've had some success with encouraging students to measure position by putting a ruler directly on their screen - but until a few days ago it was quite difficult to get useful clock reading measurements from the YouTube player.

This exercise is MUCH more powerful now, thanks to a simple online app called RowVid, originally created by Calum EadieAndrew Ratomski and Jack Lawrence Jones at an Entrepreneur First Hackathon to help rowers analyze training and race videos. Since then, it has developed into general purpose player for frame by frame and slow motion playback of any YouTube video. When I first stumbled across the player, I got in touch with Calum by Twitter and mentioned to him that the player would be even more helpful for physics classes if it displayed the clock reading of the frame. He made this modification in a matter of hours - AND included in the display an estimate of the uncertainty of the clock reading! In a follow-up email, he mentioned to me that he's "keen to hear how it's being used and are very open to feedback from teachers on how to make it better. Get in touch by tweeting @CalumJEadie." This invitation is open to anyone, so please don't hesitate to make your comments and suggestions known!

A ruler on the screen is perhaps not as accurate as point-by-point video analysis, but it's also much less black-boxish. Students are forced to declare their own reference point and positive direction by placing the ruler on the screen. They see first-hand how to think about a "reference point" when the camera is moving along with the subject, and forced to think about what reference lengths they might use in the frame to scale their measurements to usable values. In other words, they have to everything that they have to do in real video analysis software, but they have to do it by hand - and thereby come to terms with why these steps are important.

For example, one of the essential elements of the "Constant Velocity Particle Model" unit in a Modeling Instruction sequence is determining whether the analytical tools in the model are useful for describing the motion of an object. In my ninth grade class, I've shown students following video of sledders at Brooklyn's Prospect Park with the following prompt:

Choose a sledder in the video. Is the CVPM useful for describing the sledders motion? Collect and graph position data directly from the video to defend your answer with evidence. If you can, estimate the instantaneous velocity of the sledder at one clock reading.

Now I can link directly to the video in RowVid's frame-by-frame player, so students simply click on the link to begin analyzing the motion. Here's a picture of me collecting data on the motion of a sledder in the video. 

I chose somebody on a yellow sled who whizzes by at about t = 13s. When I assume that the sled is about 1.2m long, I get a constant velocity of 5m/s for the 1s time interval. Seem reasonable?

What applications do you see for frame by frame video analysis in your classes? Is analyzing "real-life" motion a theme in your class? What skills does this require that solving "constant velocity" problems from a book or worksheet don't address?

FYI - RowVid is currently working on a version of the app focused specifically on the Sochi Winter Olympics. Let's hope that there are some clips where the camera is steady!

Continue reading →