“Five in the pool, I’ll show what I can do, belly clapper, ouch, ouch,” the band wrote Your friends – and this catchy song line alone is enough to grimace painfully. After all, the vast majority of people have had the opportunity to experience first-hand how an accidental jump into the water burns and how unpleasantly hard the water surface can feel if you don’t approach it smoothly.
Physicists at Cornell University in New York have now used 3D-printed dummies to test the jump height from which the human body is actually likely to sustain injuries when hitting water. To do this, the researchers built models for three different postures: one with the head first, a second with hands above the head and palms touching, and another model that consisted of one leg with one foot that was supposed to represent the straight jump into the water.
A dummy diving in, arms first.
(Photo: Cornell University/Cornell University)
The models were equipped with a force sensor and filmed with a high-speed camera during water impact. Subsequently, the measured hydrodynamic forces, which primarily arise from the impact, were related to the critical compressive forces known in the literature for human muscle and bone injuries.
The world record for a foot jump is almost 60 meters
The result: when jumping head first, it becomes critical for the spinal cord and neck from a jump height of eight meters; if the hands are the first to go in, the main risk of injury is the collarbone from a height of 12 meters, and straight jumps with the feet risk knee injuries from a height of 15 meters.
Head first, hands back is risky even from a fairly low height.
(Photo: Cornell University/Cornell University)
The fact that professional high and cliff divers dare to jump much higher and usually survive unharmed is in turn due to the technique of the professionals. By tensing the right muscles, they keep their body stiffer and stronger. Body tension is generally a good idea when jumping, and not just for professionals. The perfect immersion position is also crucial. The current world record for a feet-first jump, for example, has been 58.8 meters since 2015. However, the extreme athlete Lazaro Schaller suffered a torn inner ligament.
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Animals have an even better technique. In addition to the human models, the New York scientists also printed and researched the head of a porpoise, the beak of a northern gannet and the foot of a basilisk lizard. So while humans howl in slow motion from the edge of the pool after a stomach flop, the gannet, for example, which dives into the water at the enormous speed of 24 meters per second when hunting, uses a dense layer of feathers on the back of its head to absorb the impact force on its long, flexible neck, which then bends.