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Re: [Phys-l] An intersting integral calc. problem.



Though I have not had access to suitably qualified stage magicians,
like John M. I am also skeptical of too ready acceptance of movie clips.
...Of impacts, or of high wire linesmen.

I started by looking for an error on the face of it - as lawyers are wont to say.

It turns out the frame rate and the golf ball speed are both plausible, as
one may verify by checking the time required for the ball to move one radius
before impact, and noting that Titelist puffs mention initial ball speeds of
150 - 160 mph among other sources and that very high speed cameras
can run a few frames at millions of frames per second.

It soon becomes evident that the rebound speed is WAY less than
0.85 X 150 mph, and it is not difficult to see why.
The impact plate rebounds sharply, though this is masked at left of the image.

Hence the dwell time one might apply is WAY too long: this essentially
confirms that John M's force estimate is a proof by contradiction.

The force applied to the initial impact area is so large, that a core volume is
rebounding while a toroid is still approaching the plate - which recedes
(out of view) during the flattening images.

Brian W

On 7/7/2010 7:31 PM, John Mallinckrodt wrote:
I'm skeptical. If it DOES flatten that much, the time of impact is
considerably longer than it might otherwise be, thus reducing the
average force. For a complete flattening, I get an average force of
something like mv^2/(2d). With m = 50 g, v = 150 mph, and d = 4 cm,
this gives something like 3 kN, it seems to me that I can pretty
easily apply a static force of 1 kN (e.g., by standing on the ball)
and I'd expect to see very little compression. So, as I say, color
me skeptical.

On Jul 7, 2010, at 3:08 PM, Bernard Cleyet wrote:

http://www.flixxy.com/golf-ball-slow-motion.htm

Golf Ball Hitting Steel At 150mph - Slow Motion (70,000 fps)