MAT 136

# MAT 136, Falling Ball

The YouTube video shows a falling ball, taken in slow motion.

Estimate the speed of the ball when it is at the 45 cm mark, near the middle of the frame.

The video was taken in SLO-MO mode, at 240 frames per second.

To step one frame at a time on a laptop, pause the video and then type period (.) to step forward or comma (,) to step backwards. The playback is at 30 frames per second on YouTube. (Actually it is 60 frames per second and it plays each frame twice.) The settings tab in YouTube gives some useful information.

I find that this one-frame feature is not very consistent across platforms. I usually have to press the period key twice for every frame. On my laptop it sometimes jumps two frames, but on my windows desktop and my iMac desktop it is reliably 2 key strokes per frame.

I don't know how to step one frame at a time on my iPhone. Let me and the class know if you figure out how to step one frame at a time on your phone. I may give you extra credit!

As a very rough estimate of the speed, it takes about 0.5 seconds to go 10 cm. in slow motion. The slow-down factor is 280/30 = 8. So the speed is rougly 10cm/(0.5s)*8 = 160cm/s. If your answer differs by a factor of 2 or more from this ball-park estimate, you are doing something wrong.