I’m wondering if the “throw something in the water just before you go in” trick works not because of the surface tension but because of cavitation – that is, it essentially adds a lot of bubbles to the local area, reducing the density and increasing the compressibility of the water.
Don’t get me started.
The thread Osiris linked to has links to all other threads on this in which I have participated.
When high speed water skiing, it is wise to never put your arms out in reaction to falling which is very easy to do, speed skiing is like trying to balance on oiled bouncing glass. I have only gone down at 70+ MPH and did remember to tuck into a tight ball, made six skips and slid across the surface a loooong way. Another skier went down the same day and stuck his elbow out only a little bit. Took his shoulder out of socket.
Do a frog with a webbed or wings jump suit and T.V. is a good bit less and horizontal movement is much greater, might get lucky… Some Frenchy was gonna try to hit a grassy slope of the right degree. I have not heard if he ever really tried, but he was practicing with the webbed jump suit.
Finagle’s right, the point of throwing something heavy into the water right before jumping is to create alot of bubbles in the water where you will hit. The air in the bubbles is very compressable and allows the water enough room to displace as you enter it. Water isn’t compressable and so jumping into a calm pool requires the water to move out of the way, which it can do only so fast and under much duress.
I’m having trouble finding a cite for this, but during the construction of the Sydney Harbour Bridge (opened 1932), there were quite a few workmen who lost their lives in falls. The only one to survive was a guy whose toolbox hit the water a moment before he did. He suffered fractures, and IIRC, his boots somehow “welded” themselves to his feet.
Guys, when I was a kid I was given a “Guiness Book of Records” as a Cristmas present. And being the lover of useless trivia that I am, I memorised literally hundreds of facts.
One in particular was a Russian pilot who bailed out of his prop driven fighter near the end of WW2 from about 29,000 ft - with no parachute! And he lived!
The article quoted that the pilot bailed out over incredibly forest which was covered by powder snow and he hit the powder snow on one the tall pine trees in his landing zone - he bounced thru about 80 ft of branches and came to a relatively soft landing believe it or not and survived to tell the tale.
I must say I like the idea of the cavitation bubbles. In theory, a huge bubble making device straight under your dive zone could make a huge difference.
Another bizarre question is this… if you were in a specially designed steel diving javelin, how high a dive could you survive from? Gotta be a few miles surely! Imagine the terminal velocity on something like THAT! More importantly, how deep would one of those suckers go before trying to resurface!
>> They jump, point there toes, lock there body and almost all die
That’s neither here nor there, is it?
Well if at 200ft you have a very high mortality rate then I believe we have a very good upper limit for the OP. Most definately at 200ft you can not safely jump into water.
And if you’re an average Joe then I would strongly urge you not to attempt to claim those world records Telemark mentioned. I’m sure those record holders were not only fit but had trained quite a bit to make those records.
I remember seeing something before the Winter Olympics about how ski-jumpers were able to practice without snow by jumping into pools. The only catch was that the pools had to have air pumped up from the bottom of the pool so that the skis wouldn’t break. So I think that supports the idea of cavitation increasing the compressability of the water.
Water is not compressible, soil is…
Water is. How do you think firehoses work?
You’re right water is compressible, but not a whole lot…
from
http://www.sbu.ac.uk/water/explan.html#comp
It may be thought that water should have a high compressibility (kT = -[¶V/¶P]T/V) as the large cavities in liquid water allows plenty of scope for the water structure to collapse under pressure without water molecules approaching close enough to repel each other. The deformation causes the growth in the radial distribution function peak at about 3.5 Å with increasing or pressure (and temperature), due to the collapsing structure. The low compressibility of water is due to water’s high density, again due to the cohesive nature of the extensive hydrogen bonding holding. This reduces the free space (compared with other liquids) to a greater extent than the contained cavities increase it. At low temperatures D2O has a higher compressibility than H2O (e.g. 4% higher at 10°C but only 2% higher at 40°C) due its stronger hydrogen bonding producing an ESCS equilibrium shifted towards the more-open ES structure
Water isn’t compressible to any great extent. Bulk modulus for Skydrol hydraulic fluid is 200,000 psi, and although I don’t have a number for water, I’m guessing that it’s pretty close to that since the densities are similar.
However, a little bit of dissolved air makes a big difference; in our hydraulic systems, the effective bulk modulus is only about 80,000 psi, almost entirely because of dissolved air.
Firehoses work because you have a pump pushing the water out the open end of the hose. Compressibility doesn’t enter into it at all.