Running across water has long been a staple in myths and fantastical stories, captivating imagination with its seemingly impossible nature. Exploring the scientific principles behind such a feat reveals the complex physics that govern interactions with water and the extraordinary demands it would place on any living creature.
Understanding the Physics of Water
Water, despite its fluid nature, offers resistance that can be harnessed to support weight. Moving across its surface relies on several physical principles. While surface tension allows lightweight insects to “walk” on water, this force is entirely insufficient for a human. Larger objects need hydrodynamic lift, a force created by rapid movement through a fluid. This is the same principle that allows a boat to plane across the water or an airplane wing to generate lift.
To run on water, an individual must apply enough downward force very rapidly with each stride, pushing the water away before it yields. This rapid transfer of momentum from the foot to the water creates an upward thrust. Like skipping a flat stone, its speed and angle of impact allow it to bounce off the surface multiple times before sinking. Water’s viscosity, or resistance to flow, plays a role in how much force can be generated. For a human, the challenge lies in generating sufficient force to overcome gravity in the fleeting moment each foot contacts the surface.
The Speed Required for Water Running
Scientific calculations estimate the immense speed a human would need to run on water. To generate enough hydrodynamic lift, an average adult would need to run at speeds from 67 to 119 miles per hour, depending on body weight and foot size. This velocity is far beyond human capabilities; the fastest sprinters reach closer to 28 miles per hour.
The basilisk lizard, often called the “Jesus Christ lizard,” provides a real-world example of water running. These lizards sprint across water at 3.3 to 3.6 miles per hour, taking up to 20 steps per second. Their technique generates a rapid downward force with each footfall, creating an air cavity that momentarily supports them. The power required for a human to replicate this feat is calculated to be about 15 times greater than a human’s maximum sustained muscle output, making it practically impossible.
Human Limitations and Biological Differences
While the theoretical speed for running on water is daunting, human anatomy presents significant limitations. Unlike the basilisk lizard, which possesses large feet with fringes that spread to increase surface area upon impact, human feet are relatively small and not designed for such action. This limited surface area means a human foot would simply displace water without generating enough supporting force. Even if a human could reach the necessary speed, their small foot size would make it extremely difficult to create the required upward thrust.
The mechanics of a basilisk lizard’s stride are highly specialized. Their legs act like pistons, rapidly slapping the water, pushing down and back to create a temporary air pocket that provides lift before quickly recovering the foot for the next step. Humans lack the muscle power and specific limb structure to perform this three-phase “slap, stroke, and recovery” gait with the necessary speed and force. Our muscles are not capable of the rapid, powerful contractions needed, meaning our natural running mechanics would cause us to sink rather than skitter across the surface.