Decided to measure empirically. Turns out if you just drop it, very slowly!

Note: daylight was critical for slow mo video.

First off, rotational inertia was not a negligible component as it turns out. If you drop something side-by-side with the yoyo, the yo-yo falls suppppeerrr slowly. Here is my awesome roomie showing this (using samsung galaxy s9 slow-mo — online says it should be 240 fps)

Second, I think the yoyo only spins about 60 rpm!!! Maybe it can be faster when thrown. But wow, my back-of-envelope calculations was an order of magnitude off. Hah!

The yoyo will be spinning fastest near the bottom of the drop. So we can take this clip and run it through ffmpeg to split out individual frames, then simply count the number of frames per revolution.

ffmpeg -i yoyo_drop_bottom.mp4 -r 30 output_%04d.png

From there I count time between spins as

9 frames
9 frames
8.5 frames
8.5 frames
8.5 frames
8.5 frames
8 frames
8.5 frames
8 frames

Now if the video is originally at 240 fps (no way to confirm this for now), and now I am outputting images at 30 fps. Then, I think each frame is covering a longer chunk of time. That is, of every 8 frames at 240 fps I only select 1 frame to get 30 fps. So 8 frames of 30 fps = 64 frames of 240 fps.

Thus we know that each revolution took 0.26 seconds. (60 sec/min / 0.26 sec/revolution) = 231 rpm. Way less than 3000 rpm!

Will have to repeat in daylight to see what the rpm is like thrown.

I’m still not certain I believe in 300 rpm either, mostly as I’m not sure how much to trust the 240fps spec and my math. Next step I guess is I should do the trivial physics problem… but probably I’ll put work toward making the yoyo happen instead.

(The yoyo is from when I took MIT 2.008. We wanted to make a yoyo that whistled as a spun, this feature didn’t work, but we still had a nice ambigram).