How fast would you have to travel to be able to run on water?
Nick Canning
Coleraine, County Londonderry, UK
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If I could hit a flat surface of water above a very deep trench at supersonic velocity, such that the impulse of my step was delivered in a time faster than the relaxation time of the water molecules, then the water surface would behave more like that of a solid than a liquid and I would bounce off it.
Unfortunately, humans can鈥檛 attain such power or reaction speeds. So, unless we use flippers with a large area to displace our weight of water, or we get inside a 鈥渮orb鈥� ball, which would allow us to walk across water at a leisurely pace, we will never run across water.
Creatures that can stand or run on water, such as water boatmen, weigh much less than humans, so can use the high surface tension of water to help support themselves. Basilisk lizards also have specially adapted and extendable webbed feet.
@DonStewards
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Are we allowed to use custard powder?
Mike Follows
Sutton Coldfield, West Midlands, UK
There are several hoax videos on the internet appearing to show people running on water, but you would need to run at least three times faster than Usain Bolt to make this a reality. commissioned by sportswear firm Hi-Tec because the athletes are actually running along a pontoon that floats just below the surface of the water, which moves subtly in response to each footfall.
Insects such as water striders can float, even though they are denser than water. This is because of surface tension, where the surface of water acts like a stretched membrane, which allows a body to float if the ratio of its weight to the perimeter of its contact area with the water is small enough. The surface tension of water is 0.07 newtons per metre. This means a 90-gram basilisk lizard would need hind feet with a diameter of about 4 metres to do the same thing.
Instead, they run on water. Their feet slap the water hard enough that it doesn鈥檛 have time to flow out of the way. It is almost as if the water momentarily acts like a non-Newtonian fluid and goes stiff. Indeed, the mixed 900 litres of water, 450 kilograms of powdered corn starch and a dash of blue dye to demonstrate that it is possible to walk across a non-Newtonian liquid 鈥� provided you don鈥檛 stop.
We would need massless shoes with a diameter of about 2760 metres in order to stand on one leg without sinking. In 1996, researchers calculated that humans would need to run at 30 metres per second to copy the basilisk lizard and would need to generate 15 times the muscle power available to humans.
Ducks and other web-footed birds run on water with the assistance of lift from their wings. These birds hint at an alternative strategy: run wearing a pair of flippers and reduce the weight of the runner to about 20 per cent of what it is on Earth鈥檚 surface.
An Italian research group won the 2013 physics Ig Nobel prize for . There is a that supports 80 per cent of his weight while he is furiously splashing water out of a paddling pool in what turns out to be a successful effort to avoid sinking.
It reminds me of running barefoot on a hot surface. In both cases, the contact time is minimised. However, while people run gingerly on hot sand in a vain effort to minimise the contact force, on water, you need to slap down really hard.
Richard Swifte
Darmstadt, Germany
Wearing ordinary shoes, you would have to run as fast as a cheetah to stay afloat. But many inventors have succeeded in walking on water using various designs of extra large footwear.
In fact, 麻豆传媒 had a fascinating article on this subject in December 2009. This described the feats of Charles W. Oldrieve, who used 2-metre-long wooden 鈥渨ater shoes鈥�. Over 20 years, Oldrieve achieved fame by walking on rivers. This culminated in 1907, when he won a $5000 bet by walking 2600 kilometres in 40 days from Cincinnati, Ohio, to New Orleans, Louisiana, along rivers.
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