How does "Professor Splash" work?


by 12markkram34
Tags: professor splash, work
12markkram34
12markkram34 is offline
#1
Apr15-12, 07:21 PM
P: 4
So there is a daredevil named "Professor Splash" who is known for diving (belly flopping) from over 30 feet into a foot or less of water. You can find more information about him below:

http://en.wikipedia.org/wiki/Professor_Splash

http://scienceblogs.com/dotphysics/2...t-of-water.php

Now the second link got me really intrigued. I have taken a mechanics course, so I mostly understand the discussion of how the work-energy theorem, impulse, etc. work in his jumps, but the one thing I don't understand is what realistically determines the impulse the water exerts on him.

Sure, you can take his speed, mass, and the height of the water (1 foot), and divide them to determine the impulse the water would have to exert on him to completely stop his fall, but why does the water provide that needed force? What's to say that the water doesn't just provide half the force and thus not decelerate him completely, leaving him to splatter into the ground, albeit at a reduced velocity? Is there something I'm missing here? I suppose it would have to do with the surface tension of water being able to supply up to so much force per square inch of surface area? And if so, how would you go about calculating it realistically, since realism would logically entail a stronger force for only a portion of the distance (not actually using the entire 1 foot of water in reality). How would professional physicists calculate such a thing?
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256bits
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#2
Apr15-12, 09:48 PM
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It looks as if the pool is not resting not on a solid surface but is on a pad of some sort and an air bag underneath. So while he may hit the water and make a big splash, a lot of the energy of his fall is absorbed, if that is a good word, by what is underneath the pool.
12markkram34
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#3
Apr15-12, 10:10 PM
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Oh so he's probably a phony?

DaveC426913
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#4
Apr15-12, 10:17 PM
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How does "Professor Splash" work?


Yeah, there are two thick pads under that pool - more than a foot of cushion.

Define "phony". He does what he says he does. He's not obliged to explain every aspect of it.
chrisbaird
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#5
Apr17-12, 01:32 PM
P: 617
Definitely a phony. Using the name Professor Splash instead of Professor Air Bag shows that he wants you to think he is being stopped by a foot of water, and that is where the amazement factor lies. He could just as well get rid of the water and jump onto only the air bag, but that would not be very impressive at all because then you realize that the water has nothing to do with it.

For example, if I placed a huge spring-board on the ground, covered it with root beer, than proceeded to call myself Professor Root Beer because I had perfected the technique of jumping very high off of root beer, there definitely be something deceptive in my proceedings.
DaveC426913
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#6
Apr17-12, 01:37 PM
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Quote Quote by chrisbaird View Post
... the water has nothing to do with it.
The water has about 43% to do with it.

He's got about 8" of airbag, 8" of pad and 12" of water to stop his fall.
chrisbaird
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#7
Apr17-12, 02:17 PM
P: 617
Quote Quote by DaveC426913 View Post
The water has about 43% to do with it.

He's got about 8" of airbag, 8" of pad and 12" of water to stop his fall.
Thanks, I exaggerated. But there is still an element of deception in his whole presentation that takes advantage of those less scientifically versed.
DaveC426913
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#8
Apr17-12, 03:01 PM
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Yeah, in fact, it makes one wonder if he spent a little time toying with the values to optimize the gimmick.
"Hm. I could claim to dive into one inch of water, but that would mean my airbag and pad would have to be 27 inches thick. A little obvious, even to the layperson. Or I could minimize the underlay, down to 4 inches, but then I'd have to declare I'm diving into 2 full feet of water - not so impressive-sounding... Hmmmm..."


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