To make the biggest splash when you dive-bomb into water, the secret seems to be to use the Manu technique practised by the Maori of New Zealand. This involves folding yourself so your torso and legs make a V-shape as you fall and making sure your buttocks hit the water first.
The origins of the Manu, which is Maori for bird, are unclear, but leaping from bridges, docks, rocks and diving platforms, aiming to produce the largest possible splash, has long been a popular part of Maori culture.
And those splashes can be big. The winner of the 2024 Z Manu World Champs , for example.
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Now at the Georgia Institute of Technology, Atlanta, and his colleagues have studied 50 human Manu jumpers in YouTube videos to analyse what they were doing with their bodies to send so much water flying into the air.
They also created a mini 鈥淢anubot鈥�, weighing just 115 grams and which could quickly open its body to mimic human Manu movements, and tested it in the laboratory.
Rohilla and his colleagues found that a human Manu comprises four distinct stages: water entry in a V-formation; a roll back and kick motion underwater to enlarge the air cavity; the closure and collapse of the air cavity; and then the creation of what Manu jumpers call a 鈥減op鈥� or splash.
鈥淲hen a solid object, including humans, falls or jumps into water, it pushes water away and creates a large air cavity,鈥� he says. 鈥淭he pushed-away water decelerates and then accelerates inward, driven by buoyancy force and meets at the centre with high velocity, which is called cavity collapse. The convergence of the flow generates a powerful vertical liquid jet known as the Worthington jet.鈥�
That Worthington jet is the pop, says Rohilla, and it is the opposite of what Olympic divers try to achieve when they minimise their splashes on entry to the water.
The researchers found that, to maximise the splash, the ideal angle of the V-shape the body makes when entering the water is 45 degrees. The other key tactic is to open the body at the right moment underwater.
鈥淚f an average man, 1.75 metres tall, falls from a height of 1 metre, his impact speed is around 4.43 metres per second,鈥� says Rohilla. 鈥淭he optimal body opening time of 0.26 to 0.30 seconds from the start of falling will generate the most powerful Worthington jet.鈥�
bioRxiv
