How does jumping off a bridge into water kill you?

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4 Replies to “How does jumping off a bridge into water kill you?”

  1. It is possible that, in many cases, it is the impact that kills you, as hitting water at sufficient speed will subject vulnerable body parts, such as the head, to severe deceleration forces that could potentially be fatal (through, for instance, causing a broken neck, leading to a basal skull fracture and severing of the spinal cord from the brain stem, as in the case of execution by hanging, or high-speed frontal impact car accidents).

    It is also possible, in the case where a person impacts the water horizontally and face-down (i.e. in a 'belly flop' position), that the sudden compression of the abdomen as it hits the resisting water surface could cause shock waves to radiate through the body from the abdominal cavity (like being punched or kicked very hard in the stomach), causing a sudden increase in blood pressure in critical blood vessels leading to the brain, and death through instantaneous and massive brain haemorrhaging. It is thought that this might be a frequent cause of death from high-velocity gunshot wounds to the abdominal and thoracic cavities, an effect known as hydrostatic shock (…),

  2. Well, let's look at the force of impact (granted it is in water, and calculating the true impact is quite complex)… nevertheless.

    Let's take the Golden gate bridge for instance:

    67 meter fall/jump.
    Weight of jumper: 70 kg

    Let's ignore air resistance:

    We're left with:
    Acceleration = -9.8 m/s^2

    Vf^2 = V0^2 + 2*a*h
              = 0 + 2 * (-9.8) * 67

    Vf = 36.24 m/s or 130.46 km/hr or 81 mph or 119.592 feet/s

    F = ma = 686N

    Since we're jumping into water, let's calculate the deceleration upon impact into water.

    Impulse = -(70kg * 36.24m/s) = 2536.8 N . s

    Ignoring terminal velocity and such (since it is 81 mph), so now it is just a matter of how you fall into the water to account for the amount of deceleration from the impact depth your body suffers.

    We can assume that the density of a body is almost equal to water (considering we're made up of roughly 3/4 of the stuff, and we float).

    Impact depth = Length * (Density of body A / Density of the medium B)

    So the impact depth is roughly the length of your body (plus a bit more).

    For example: You were unlucky enough to fall perfectly horizontal.
    This means the entire force of impact would cause your body to decelerate to half the velocity in about a foot of distance.

    So at around 120 ft/sec, passing 1 foot of depth would take 1/120 = 0.008 seconds

    Duration of impact would be 0.016 seconds:
    Average Force = Impulse / dt = 2536.8/0.016 = 158550 N or 16 Tons.
    Deceleration = Average Force / mass = 158550/70 = 2265 m/s^2 or 231 gs

    Highly doubtful you'll survive.

    Now if you were lucky enough to fall feet first and perfectly vertical.

    Impact depth = (let's assume the person was 6 ft tall).

    So 6/120 = 0.05 seconds

    Duration of impact would be ~0.1 seconds:
    Average Force = 25368 N or 2.6 Tons.
    Deceleration = Average Force / mass = 25368/70 = 362.4 m/s^2 or 37 gs

    If you did survive, the impact would be enough to shatter all your bones from your feet to your hips. There may be significant damage to your vital organs as well.

  3. A grisly and informative article about suicides from the Golden Gate bridge can be found at the New Yorker. For a fall itself to kill, the required height that a bridge must be at least 250 feet.

    Apologies for quoting their source at length:

    "The coroner’s usual verdict, suicide caused by “multiple blunt-force injuries,” euphemizes the devastation. Many people don’t look down first, and so those who jump from the north end of the bridge hit the land instead of the water they saw farther out. Jumpers who hit the water do so at about seventy-five miles an hour and with a force of fifteen thousand pounds per square inch. Eighty-five per cent of them suffer broken ribs, which rip inward and tear through the spleen, the lungs, and the heart. Vertebrae snap, and the liver often ruptures. “It’s as if someone took an eggbeater to the organs of the body and ground everything up,” Ron Wilton, a Coast Guard officer, once observed.

    Those who survive the impact usually die soon afterward. If they go straight in, they plunge so deeply into the water—which reaches a depth of three hundred and fifty feet—that they drown. (The rare survivors always hit feet first, and at a slight angle.) A number of bodies become trapped in the eddies stirred by the bridge’s massive stone piers, and sometimes wash up as far away as the Farallon Islands, about thirty miles off. These corpses suffer from “severe marine depredation”—shark attacks and, particularly, the attentions of crabs, which feed on the eyeballs first, then the loose flesh of the cheeks. Already this year, two bodies have vanished entirely."

    Read more

  4. Depending on the height of the bridge, of course, it's primarily the impact. Water is dense, and hitting it at speed is a hugely traumatic force. In the event that it doesn't kill you, drowning due to injury or general shock is a high likelihood.

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