For centuries, humans have floated the idea that we might, one day, walk on water. In the 15th century, Leonardo da Vinci invented a pair of pontoon-like shoes intended for this purpose, and in 1988, French entertainer Remy Bricka walked across the Atlantic on a pair of floating skis.
Perhaps we were inspired by nature – more than 1,200 species of animals can walk on water. The smaller ones, such as insects and spiders, use surface tension, the force that holds water molecules together, to support their weight. These forces are much too weak to support the weight of larger water walkers, such as the basilisk lizard, which generates force to stay afloat by slapping its feet on the water.
But for a human to run across the water like a basilisk lizard, he would have to sprint at about 67 mph (108 kph), nearly as fast as a cheetah, according to a 2006 paper in the Annual Review of Fluid Dynamics. The world’s fastest man, Jamaica’s Usain Bolt, averaged about 23.5 mph (37.8 kph) during his world record 100-meter dash at the 2009 World Championships. This feat would take about 15 times more energy than the human body is capable of expending.
But the limits of the human body haven’t kept us from dreaming. In the last 40 years, individuals have patented more than 50 water-walking devices.
So although we can’t walk on water on our own, we can cheat. These devices work in two ways – they either increase buoyancy, or they use a force called dynamic lift, according to John Bush, an applied mathematician at Massachusetts Institute of Technology.
Most of the patented devices are designed to increase buoyancy, and are a take on da Vinci’s classic, pontoon-ski design. Some have modifications such as bungee cords to keep the water walker’s legs from splitting apart, or hinged rudders for steering and stability. Most patented water-walking devices use a light buoyant material, such as Styrofoam or wood.
Dynamic lift, on the other hand, requires an outside force acting on the human body. A force is needed to pull the body in a direction parallel to the water’s surface, explained Bush.
This principle, which also describes the forces acting on an airplane’s wing, can be seen when a motorboat pulls a person along the water's surface – think of barefoot water skiing. If the feet are angled properly, water flowing past the body will effectively exert an upward force that elevates the barefooter out of the water.
Print