Secrets of Slithering Snakes

Snakes and math.

Much of the population is afraid of one, or both.

But David Hu, mathematician and mechanical engineer, combines those two sometimes scary things to unlock the secrets of how animals move.

"There's a lot of interest in animal locomotion these days, and what we can learn from the way animals walk, swim and fly," said Hu.

"It turns out their interactions with their surroundings, fluids, solids--it's very complicated. And it's complex enough that mathematics plays a very large role in understanding how they move," said the Georgia Tech professor.

In a National Science Foundation (NSF) study, Hu found that snakes slither in a different way than researchers have long thought.

For decades, researchers believed that snakes move through a forest by pushing off rocks, twigs and branches. But that did not explain the reptiles' relative ease navigating smooth surfaces.

The secret seems to be in the scales.

"The snake has these belly scales that are overlapping, and they basically push into very small bumps in the ground," said Hu. "And that small amount of force can provide enough force for the snake to move." Like wheels or ice skates, when snakes slide forward, it takes less work than moving sideways.

When they come out of their eggs, snakes instinctively know four different motions, or gaits, to navigate their world. Slithering, also known as undulating, is the most common. Snakes can also move by extending and contracting, sidewinding, and finally, a rectilinear, or straight-line motion. Hu compares the gaits to gears on a car.

"If a snake is slithering and not really going anywhere, it will say, 'OK, I'm going to go to gear two,' and gear two for them will be, instead of undulating, extending and contracting."

That is where the math comes into play. Hu and his colleagues at New York University and Georgia Tech observed snake motion and measured the friction coefficients of snakeskin. They were able to show how snake propulsion on flat ground relies on the friction of the snake's scales. The researchers' experiments also showed how snakes move: not perfectly flat against the ground, but rather by pushing down some parts of their bodies while lifting up other parts as they slither.

An understanding of snake movements is helping engineers create better snake-like robots. Georgia Tech mechanical engineering professor Wayne Book and his students have incorporated snake movements into some of their designs.

"Snake locomotion is deceptively simple," said Book. "It's not really so simple when you try to repeat it, or replicate it. But it requires a relatively simple motion that we can provide."

Snake moves can be used for military, rescue and construction robots.

"When we carry a marsupial robot on the back of another robot, it could then provide the motion of a tool, a jack that could lift up heavier objects than the robot itself could. So it can worm its way or wiggle its way under loads that need to be lifted. And so, that's the reason we are interested in that capability," said Book.

Hu not only works with snakes, he has them as pets as well. And he thinks many people fear them simply because they are so alien compared to humans.

"Having no arms and no legs seems like it would be the worst body plan in the world. But it turns out snakes use it to their great advantage and they can go into places that things with arms and legs can't," he said.

And, someday soon a snake--at least a snake robot--may work its way into a lot of people's hearts, literally!

"If, instead of opening a chest cavity, you could just drill two holes and have these surgical snake robots slither in and perform the operation, the healing time would be much faster," said Hu.

Sometimes modern technology can learn a thing or two from a simple, elegant design from Mother Nature.