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by ymusti 5116 days ago
There's another Feynman bowling ball story. He was watching a younger physics prof make the same demonstration in a Caltech lecture hall. Instead of cleanly releasing the ball, she inadvertently gave it a slight shove. Fortunately for her, Feynman saw the mistake and pushed her out of the way of the returning ball which left a mark in the wall where her head had been.
1 comments
gjm11 5116 days ago
The kinetic energy in the ball's motion when it returned to her face should have been no greater than that imparted by the "slight shove". Can't have been so very slight. (Or else leaving a mark in the wall was easier than it sounds.)

I just tried thwacking my nose with about as much force as I could reasonably describe as a "slight shove" in that situation. It wasn't terribly pleasant, but it wasn't very painful and did no damage.

I cordially doubt that the younger prof was in danger of anything very bad. Assuming that the rest of the story is true, I suspect that Feynman was either being (commendably) over-cautious or showing off. Perhaps both.

(There's a more unpleasant failure mode for this demonstration: If you move your head forward after releasing the ball, then it'll hit your nose earlier, when it's lower down, which if the ball is very heavy can mean quite a considerable amount of extra energy.)

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cma 5115 days ago
A bowling ball is inelastic; whatever you thwacked your nose with (your hand?) definitely isn't. Drop an egg 1 foot onto a carpet, then try onto concrete.
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gjm11 5115 days ago
Yes, fair comment. I don't think that makes more than a factor of 2 difference, though. When the impact happens, in one case the squashing is half in my nose and half in my hand, versus all in my nose if it's a bowling ball.

(The egg example makes things look worse than they are. If an egg squashes at all, it breaks. My nose can squash quite a bit before that happens.)

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Tichy 5115 days ago
"I just tried thwacking my nose with about as much force as I could reasonably describe as a "slight shove" in that situation"

Good to know that this kind of scientific spirit still exists :-)

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