# Maximum - free fall dive into water

by Ouabache
Tags: dive, fall, free, maximum, water
 P: 1 Ouabache: This references puts the figure at 26 surviving dives from Golden Gate Bridge. However they also state that 98% of the dives are fatal. So we should specify lethal dive heights within some statistical deviation. This is statistic is very biased though. I have also read this, and the data claimed that 26 out of approx. 1200 jumpers survived, but those 1,200 jumpers were jumping with the intent of dying upon impact, so I doubt they hit the water in a position that would help them survive the impact, i.e., as a vertical line or in a dive. Also, BMI is a variable to take into account. I would expect men to have a greater chance of surviving due to a more streamlined body, and also the outfit would need to be taken into account, as most of the jumpers in san francisco would be wearing several layers due to the cold weather. If I were to guesstimate the chance of surviving this fall while trying to survive, is much higher. With proper attire, I believe a physically fit male would probably be able to increase his chances by at least 5x, if not more. I still don't give them a great chance, but its better than a measly 2% chance of survival. While this is purely speculation, as I have not done any proper calculations, I would hope that this post at least helps someone else come to a more scientific conclusion on the matter.
 P: 28 The world record dive is available on utube 4uHkyMh9FW4 Note there is not a mark on him so clearly you can survive a good deal higher than this. My rough extimate of his entry speed is about 70 mph. (assuming no air restance). Apparently freefall velocity is about 135mph but it is a variable depending on the body shape you adopt. A freefall would at 135 would 3-4 times that impact of the dive shown.
 P: 5 Another question would be what part of the human body is considered the weakest? It makes sense to say that whatever part that may be the weakest will sustain damage the easiest, not taking into consideration any specific position whilst hitting the surface. My suggestion would be that the organs and the brain would take the most damage as they continue to move downwards due to sudden massive decelleration of the body when impact occurs. Internal damage probably occurs long before any muscle injury or "bruising" and would greatly cut the distance required to sustain damage. Would the height at which you sustain damage from when hitting for example pavement be similar to the height when hitting water? At what speed does water turn into stone?
 P: 1 What is the maximum height a person can make a free dive without incurring physical injury? I believe the height is unlimited, terminal velocity can be reached and with a perfect feet first entry keep in mind you would want to transition from a flat body position 120 mph to vertical at the last possible moment to minimize acceleration which will occur. But the most important factor here is surface tension of the water, assuming water is your choice of liquid, Diethyl ether would be a better choice when it comes to surface tension but I assume that would not be feasible. With the proper temperature the hotter the water the less surface tension, aeration of the water to further reduce tension, and the use of Surfactants (wetting agents that lower the surface tension of a liquid) example: soap. One thing I have not explored is mentioned in a previous post "acute barotrauma" not sure about this one and also not sure of the depth one would travel and would have to get back to the surface. You are bound to travel further because of the reduced surface tension. If you guys can help me figure all of this out, I'm willing to take on the challenge of pulling this off from say 10,000 feet. This should sufficiently break the current record of 172 feet.
 P: 1 Ok, I registered because I have been trying to figure this out. I think something that can allow us to gauge the answer a little better is if we determined terminal velocity of a falling human. At what distance does a 150lb human have to fall to reach terminal velocity?
 P: 41 Theres no definite answer for this problem is there? I mean people vary, and in order to solve this we would need numbers, such to turn it into a word problem. The max height would vary from person to person. A larger man would definitely sufffer from a greater impact since his surface area is greater and that he has more mass meaning the force pulling him down would be greater, acceleration equaling gravity so mass would be the only factor in this case. Now as Ouabache put it, lets assume the water is calm, meaning the surface tension would be greater. We could try to visualize this using silly puddy. The Larger man hitting the water would have about the same affect as a ball of silly puddy hitting the wall. Whereas a thinner man would be like a pencil, penetrating it easier. And of course age matters too, even if a 10 year old boy is smaller and lighter there is a greater chance that he will suffer bone fractures. It would also make a difference if the person was doing it head first or feet first where head first as Moonbear pointed out would be more susceptible to head and spine injury, this is why when the Navy(Marines? IDK) do sea rescues they always dive feet first since our legs are usually stronger than our upper body and could take the impact, and if worse comes to worse the person would only be paralyze waist down and not neck down.
 P: 1 I'm not a physicist or a biologist, but I have jumped from 40+ metres on many occassions. My opinion is that when I hit the water (always the ocean) I'm at around half the speed of "terminal velocity". I have done this barefooted, wearing diving booties, and also wearing steel capped work boots. Barefooted was OK. One time the booties (they were very old) split and ran up my leg, and the construction boots were untouched. I'm pretty carefull. I always go feet first (of course) and have always instinctively raised my arms straight over my head just before entry. My feeling is that if I were to enter the water at twice my current speed (which I reckon would be close to a skydiver's speed), I would be fine. It is all about "slipping in" like an arrow. There are plenty of sea birds that enter the water at absolutely astonishing speeds, but because they streamline themselves so well, it does them no harm. In my opinion, if you do it right, you can jump from virtually any height and land in water safely.
P: 107
 Quote by Ouabache That's interesting, so i also did a little digging.. This references puts the figure at 26 surviving dives from Golden Gate Bridge. However they also state that 98% of the dives are fatal. So we should specify lethal dive heights within some statistical deviation.
Your source is overlooking that many (I would say 100% of them but thats just me) people who die from jumping off bridges die from Hypothermia and drowning.

With the Golden Gate Bridge it's more a matter of being able to save the jumpers who've landed in water and are then paddling around in the water shocked and confused and freezing in the nick of time before they drown. Those ones that get picked up probably survive but this isnt about surviving the impact so much as not drowning in the water. It's very cold in the bay and I doubt the response time is that fast either. This is what I think the jumpers don't understand.. they are drowning themselves and they might end up treading water until they freeze to death and get exhausted and drown. that is not an easy or fast way to go. Even though a suicidal person would seem to give up many do fight for their lives after landing in water from a high drop.

My friend's roomate was seen dog paddling and attempting to swim and trying to survive for many minutes after he jumped and he eventually drown before a rescue boat could arrive. He leapt from some tall bridge in florida apparently. That scenario is common from suicide by bridge.
P: 2
Glad to see other people are thinking about this! I've had this crazy idea of jumping from space into the ocean without a parachute, and I'm trying to figure out how feasible that is. I'm especially interested in tokyosteve's comment:
 Quote by tokyosteve I'm not a physicist or a biologist, but I have jumped from 40+ metres on many occassions. My opinion is that when I hit the water (always the ocean) I'm at around half the speed of "terminal velocity".
I am a physicist, sort of, and I can tell you that your intuition is a little bit off, but not drastically. In freefall (no air resistance), your speed at impact from any height h would be the square root of h*g, where g is the acceleration of gravity near Earth's surface. In metric, that's 9.8 m/s2, so from 40 m, you'd be hitting at 28 m/s, which is almost exactly half of a typical skydiver's terminal velocity of 195 km/h or (insert unit conversions) 54 m/s. However, from 40 m, you're going to encounter significant air resistance on the way down, so your actual velocity on impact was somewhat less than half terminal velocity. When it's not so late, I'll make a more exact calculation of your impact velocity that takes air resistance into account.
 I have done this barefooted, wearing diving booties, and also wearing steel capped work boots. Barefooted was OK. One time the booties (they were very old) split and ran up my leg, and the construction boots were untouched. I'm pretty carefull. I always go feet first (of course) and have always instinctively raised my arms straight over my head just before entry. My feeling is that if I were to enter the water at twice my current speed (which I reckon would be close to a skydiver's speed), I would be fine...
That's very encouraging.
 In my opinion, if you do it right, you can jump from virtually any height and land in water safely.
That's my conjecture too (with the caveat that "doing it right" may involve a semi-rigid full-body suit), but I'm nowhere near convinced yet. Skydivers reach terminal velocity after about 150 m, but that's in belly-down orientation (maximizing the force of the air). As tokyosteve points out, to enter the water safely, you'd want to enter feet-first (minimizing the force of the water), so you'd need a couple seconds to transition; at 54 m/s, you cover another 100+ m in that time. So if someone does it from 300 m, I'll be convinced it can be done from any height.
P: 3,387
 Quote by tokyosteve In my opinion, if you do it right, you can jump from virtually any height and land in water safely.
I assume by "do it right" you mean - "with equipment that takes the impact so your body doesn't"?

There is going to be a maximum velocity at which you could strike water before it's effects become akin to 'slapping custard'. Whether or not that speed is greater or less than terminal velocity is another issue and something I'd think would be unique to each person.
 P: 1,070 seems like you could collect some useful data simply by dropping euthanized test animals (or a visit to the slaughterhouse if this is too much paperwork) from sufficient height. there would be a lot of tumbling, but you'd get an idea of worst-case breakage.
 P: 2 I think what tokyosteve means by "doing it right" is entering the water with proper form, i.e. feet first, toes pointed, head and arms straight up. That much would be absolutely necessary. But I suspect that yes, doing it right also includes having some sort of protective suit to distribute the impact across your body and protect against whiplash. As for the animal tests--you might get a worst-case picture, but we already know what that is from people jumping from much lower heights. If you do it wrong, you die, from some sort of rupture or the subsequent bleeding. We're looking instead for the best case--is it possible to NOT die (or be seriously injured) entering the water at terminal velocity? Or, the way it was originally posed: what is the maximum height one can fall into water from without serious injury or death? But if you can survive a terminal velocity entry, then there's no upper limit.

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