Naked Science Forum
General Science => General Science => Topic started by: vj_tu on 15/01/2006 13:02:10
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I have seen this fron CSI New York.They said even a drop of water seeped from a plane can becomes an ice when falling from a plane and travelling through air with high speed.This ice particle can hit and crack someone's head to death.
Why is so?It seems surreal for me.I think ice is very light and its travelling is against air resistance so this should slow down the speed of ice so it shouldn't cause any harm.
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I would have to agree with you as hailstones must be falling at their terminal velocity, so basically if a hailstone of a certain size won't do you permenant damage than the drop of water from a plane shouldn't either.
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Could it have something to do with the shape of the ice? Hailstones are round but a piece of ice falling from a plane could be sharp, especially if friction with the air helps to make it pointed. Plus I think I'm right in saying that a long, pointed piece of ice would fall faster than a round hailstone due to aerodynamics.
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Hailstones can kill you, it all depends on how big they are. Not often we get deadly hailstones, but I believe on very rare occasions it can happen.
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Hailstones can get bigger than a drop of water as the water will be broken up by surface tension, while it is still liquid, into lumps that are of a similar size to hailstones that hurt when they hit me but definitely didn't kill me.
If it was aerodynamically likely that lumps of ice turned into long thing needles, wouldn't a hailstone turn into one as it fell? Also long thin things tend to fall more slowly as they are unstable and will tumble.
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quote:
Originally posted by daveshorts
Hailstones can get bigger than a drop of water as the water will be broken up by surface tension, while it is still liquid, into lumps that are of a similar size to hailstones that hurt when they hit me but definitely didn't kill me.
If it was aerodynamically likely that lumps of ice turned into long thing needles, wouldn't a hailstone turn into one as it fell? Also long thin things tend to fall more slowly as they are unstable and will tumble.
I don't believe that waste dropped from aeroplanes would form needles, although there are clearly differences in the formation of ice in such circumstances and the way ice forms in clouds. Ice within clouds will generally freeze rather slowly, whereas an aircraft flying at high altitude can have an outside temperature as low as -50 C, that can freeze water very fast.
That having been said, looking at some of the information of modern airliners, it does seem they do not deliberately dump human waste into the atmosphere, but store is and dispose of it upon landing.
Hailstones have been recorded as weighing as much as 1Kg (Bangladesh in 1986), which I would imagine if it were to hit a person could be capable of killing them.
http://news.nationalgeographic.com/news/2003/08/0804_030804_largesthailstone.html
http://www.bbc.co.uk/cbbc/eurekatv/big_hailstones.shtml
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http://hyperphysics.phy-astr.gsu.edu/hbase/airfri2.html
""
Hailstone Terminal Velocity
Contributing to the danger of large hailstones is the fact that they fall faster than small ones. That is, the terminal velocity increases with the size of the hailstone. Assuming the hailstones to be spherical and using a drag coefficient of C = 0.5 gives the following :
Radius (cm) v (km/hr) v(m/s) v(mi/hr)
1.0 69.5 19.3 43.2
2.0 98.3 27.3 61
3.0 120 33.4 74.8
5.0 155 43.2 96.6
10.0 220 61 136 ""
http://hyperphysics.phy-astr.gsu.edu/hbase/airfri2.html
Energy = 1/2 x mass x (velocity)^2,
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quote:
Hailstones have been recorded as weighing as much as 1Kg (Bangladesh in 1986), which I would imagine if it were to hit a person could be capable of killing them.
When I lived in Uganda we used to get massive hailstones. I remember after 1 particularly heavy storm, my Landrover looked like the surface of the moon; as if someone had attacked it with a ballpien hammer. I dread to imagine the force the hailstones were coming down with to do that. I'm quite glad I wasn't outdoors in it!
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If were talking about a single droplet of water which will probaly measure 5mm approx total diameter even when frozen, this ice droplets terminal velocity will be only just over 10 miles per hour (sorry brit measurments here) according to the chart provided by Robert. Thats not even as fast as if someone threw it at you with mild/intermediate effort. Only just enough for you to react with "Cor blimey that 'urt me noggin guv'ner". Not even enough to cause bruising let alone kill you
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quote:
Originally posted by DoctorBeaver
my Landrover looked like the surface of the moon
well that's it !..I'm cancelling my summer hols to the Copernicus Crater if the weather is going to be inclement.
Men are the same as women.... just inside out !!
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some one posted a pic on this site a while ago with a car in germany? that had been trashed by hailstones and if it could dothat much damage to a car then why couldnt it kill you
"Defender of the Sea"
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found this on the cnn site
Softball-size hailstone kills man
Another victim of the storms, Juan C. Oseguera, 19, died Wednesday afternoon at Harris Methodist Fort Worth hospital. He had suffered severe head injuries when he was hit by a softball-size hailstone in Lake Worth.
there you go
"Defender of the Sea"
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The issue with water leaking from an airplane is not the same as frozen rain. Obviously, frozen rain does not kill, otherwise most of us would be dead already. It's also not hail, since that is a special case and forms only in thunderstorems with large updrafts.
The real danger is that water can leak from the dump valve in the airplane, and freeze as it is coming out of the pipe that is normally used to empty the privies on the ground. The slipstream can form this into an icicle, wit a very pointed end. Then it can break off and plumet to the ground. This would be called "blue ice" because of the blue color of the disinfectant in the water. There have been press reports of these icicles crashing to the ground, and weighing up to 70 pounds. It is not procedure to dump the blue water in flight, at least over land.
"F = ma, E = mc^2, and you can't push a string."
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its most probably because as it comes down it gains enough velocity that its momentum is 1000s of Newtons.
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can i take it back to the original question here, if A DROP of water.... obviously frozen water the size of a softball could kill someone if you dropped it from 100 feet, let alone 33,000 ft, but like i said one drop is going to measure about 1/5 inch across so its terminal velocity will stop it from gaining enough momentum to damage you too badly.