Can I get forty comments on this video? The rest of this post (which I'll update after we cross that threshold) depends entirely on the modal answer to the question, "what question perplexes you about this video?" Ask your own question before you look at the others.
My advance prediction for the responses was a million-way tie for third place with these two responses taking the top two spots:
- How fast was the car moving?
- How many frames were on the wall?
I couldn't guess which would win and, in terms of our mathematical objective, it doesn't matter. Both questions are tightly interwoven. (Many commenters, in fact, asked both questions.) It mattered to the production company, though. One is its premise. The other is its conclusion.
The results, through Yaacov's comment:
Sarah Cannon: "How fast is the car driving?" +25 related
mirjam: "how many pictures?" +16 related
Brent Logan: "How did the car jump? There wasn't even a ramp." +7 related
Other questions. +7
The behind-the-scenes video is less helpful than you'd imagine so I spammed basically every production company that had anything to do with the ad, asking them for information. Everyone was extremely helpful (why is this such a revelation?) and eventually my query was routed to Peter McAuley, the visual effects supervisor, who dropped a pile of knowledge on me, which I've uploaded here and which he cross-posted in the fourth comment here.
Important questions your students may have to reckon with.
- How does this effect even work? More to the point, how does film work. The camera on the outside of the car is taking photos very quickly — at a rate of 24 frames per seconds. When they're played back, our brains interpolate the rest of the motion and it looks smooth.
- Did the production company decide on the size of the frames and then figure out the speed or did they know the speed they wanted and then determine the frames? The production company figured the faster the speed, the more exciting the effect. At a certain speed, though, even the best digital sensor produced a "rolling shutter" effect (excellent animated explanation here) so they went with film, which looked good up to 40 kph. Which, bingo. That figure is crucial to every question.
- How long is the actual ad? This is the extended cut of a TV spot that ran for thirty seconds.
Start with discussion, brainstorming, estimation.
What's your guess? How many frames do you think you saw fly by? How wide do you think each picture had to be? Give a number you know is too high / too low.
Gradually apply the mathematical framework.
Ideally, either on their own or throughout the class discussion, your students will realize they need a) the length of the ad [30 seconds], b) the speed of the car [40 kph], and c) the shutter speed of the camera [24 frames per second].
From there, the dimensional analysis is up to you and your students.
Show the answer.
Download the goods.
Zipped archive [135.2 MB] containing:
- the extended commercial,
- the behind-the-scenes video,
- a PDF of the Peter McAuley's e-mail.