Snakes on a Plane

Dr. LaDuke of the Biology Department holding a milk snake. Photo Credit / Zack Gotthardt
Dr. LaDuke of the Biology Department holding a milk snake.
Photo Credit / Zack Gotthardt

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Recent studies have shown that snakes alter their movements depending on a surface’s friction. Typically, terrestrial snakes push their bodies against the ground and are able to propel themselves forward using the friction created by their scales.

In 2009, researchers at Georgia Tech tested the friction experienced by snake scales when the snake slithers across a surface. When sliding an unconscious snake forward, there was little resistance.

When slid backward, the friction created by their scales resisted the movement.

David Hu, a mechanical engineer at Georgia Tech, said, “As we were waking [the snakes], we could see them twitching individual scales.” Hu went on to compare the connection between a snake and its scales to goose bumps on human flesh.

From their research, a friction coefficient was determined and used in computer simulations for how a snake may move on different surfaces. The friction coefficient relates the force between two objects and the force of friction.

In his recent article “Optimizing Snake Locomotion in the Plane,” Associate Professor Silas Alben of the University of Michigan stated, “When the curvature of the snake backbone is prescribed as a sinusoidal traveling wave, high speed and efficiency is obtained when the coefficient of transverse friction is large compared to the coefficient of forward friction.”

While Hu’s study highlighted the importance of friction in snake locomotion, Alben’s study has determined that the strength of the friction also influences the type of movement.

“It depends on the environment that the snake is moving in. If the snake has a large coefficient of friction in the direction perpendicular to its body axis, then it will do the retrograde motion. If the friction in that direction is much smaller, it will switch to the direct-wave motion,” said Alben.

Alben developed a two-dimensional model of the motions across a flat surface, or plane. The direct-wave motion is what is typically thought of as the “side-to-side” method of movement, including wave-like transverse undulations. The direct-wave method is utilized when friction is low.

Usually, the waves on the snake’s body ripple backward as the snake moves forward, a phenomenon known as retrograde traveling wave. This method is utilized when the snake’s friction with the surface is high.

In addition to helping us learn more about our reptilian friends, these studies may find their way into robotics research in the near future.

Alben said, “A lot of researchers are building robotic snakes, which are usually a bunch of linked segments where they control the angles between the links over time…Understanding what kind of motions are optimal can help people design robots that work efficiently.”

Recently, robotic snakes have been used to inspect the pipes of a nuclear power plant in Austria, reducing the risk of radioactive contamination faced by workers. Prototypes are also being deployed in search and rescue missions, as the robots can maneuver through collapsed buildings and mines.

Some of the snake’s highest speeds and movements have not yet been explained, although studies are still being conducted to unravel the mathematical mysteries of these reptiles. According to David Hu of Georgia Tech, “Snakes have a lot of different ways of moving, sort of like a horse that can trot or gallop.”

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