Why Humans Can't Run on Water: Video Debunk

A YouTube video documenting a group of individuals running—briefly—on top of water sparked a following, and the gonzo sport "liquid mountaineering" was born. Too bad it was a hoax. Here is why you can't run on water.

Most Popular
Advertisement - Continue Reading Below

Ever wondered what it would be like to walk on water? A few sporty Europeans showed us what it might look like in a popular video launched last month. An Internet phenomenon, "Liquid Mountaineering" has received well over 4.5 million views on YouTube. Viewers wondered if it was possible, while scientists insisted it was a hoax or publicity stunt. Finally in early June, outdoor brand Hi-Tech Sports admitted they were behind the viral video and that an underwater bridge was responsible for the effect. But given the video's immense popularity, we wanted to explore the biomechanics of walking on water.

Most Popular

The video claims that special water-repellent shoes allow you to stay on top of the water. "This would only be true if the force from the water-surface tension on the shoes is enough to support one man's weight," says Eric Lauga, assistant professor of mechanical engineering at the University of California, San Diego. "Say these guys weigh 200 pounds and call g the acceleration of gravity. The surface tension of water is gamma = 0.07 N/m. If you put numbers in, you find a contact-line perimeter of 12,000 meters long. It means each shoe should be a mile long and a mile wide."

Hoax Alert: An underwater bridge is responsible for these apparent water-walking abilities.

Nor does running into the water on a curve do anything to support their weight. "However, if they could run fast enough, each time one of their feet slapped the water surface that would provide an inertial force from the water, and if they retract their feet fast enough before the water collapses, they could continue with the next foot," says Lauga, who has studied how snails can drag themselves across a fluid surface. "This is what the so-called Jesus (basilisk) lizard does."

Jamaican runner Usain Bolt, the current world record holder for the 100-meter sprint, ran 10.4 meters per second. But J.W. Glasheen and T.A. McMahon, two Harvard biologists who studied how the basilisk runs on water, found that in order to mimic the lizard, a human would need to run at almost 30 meters per second, "a velocity beyond human ability." A man would also need "an average power output almost 15 times greater than the maximum sustained power output for humans."

Devices may be able to help. "If one is dragged across the water surface at high enough speed, by a motorboat, for example, the resulting lift forces are large enough to bear one's weight; hence one can water-ski with bare feet if the boat is high enough," says John Bush, professor of applied mathematics at MIT.

Regardless of the physics involved, the video inspired. "We all aspire to not be boxed in and to push our boundaries further, to achieve the unachievable," says Ulf Gartner, who is featured in the video. "It is not about walking on water. What we do is a metaphor." But a reality check never hurts. "If man were really capable of walking on water," says Bush, "why would we have waited until now to get started?"

The basilisk lizard (Basiliscus basiliscus) weighs about 90 g and is able to run at 30 meters per second, effectively allowing it to walk on water.