Sandfish lizards jostle back and forth, bending their bodies into a slithery S-curve to swim through the sands of the Sahara. Like scorpions and several other native desert species, they long ago mastered the difficult art of moving through the myriad grains of a sandy expanse to escape predators or the blistering African sun. And now physicists are close to cracking their secrets.
Daniel Goldman’s team has been trying to figure out just how the sandfish lizards do it for years now; in 2009 they built a robot to simulate the creature’s slithering motion. This time, for a study in the Journal of the Royal Society Interface, the scientists tried to model the physics of an animal knocking around so many grains of sand and see how the lizards burrow with such efficiency.
The team found sine-wave-like movement allows the lizard, and their robot, to push forward in sand, but creating computer models for the experiments proved problematic. Simulating all of the tiny sand grains required a lot of money to purchase time on powerful computers. So, the team performed the same experiments using 3-millimeter-wide glass beads instead of sand. “We wanted something easy to simulate that had some predictive power. We got lucky, because it turned out [the lizard and robot] swim beautifully in the same way through larger glass beads,” Goldman said. [Wired]
Goldman’s simulation showed that the lizard’s impressive dive speed—it can travel twice its four-inch body length each second—depends upon slithering in just the right S-curve. If the lizards stay too straight, they don’t have the leverage with which to push themselves; if they curl too much then they can’t go fast enough. Whether the team studied the lizard in the ground, the robot lizard in a pool of beads, or the simulated lizard on their computer screens, the forces and angles agreed to within 8 percent or so.
And if we can elucidate how animals swim through sand, perhaps we can use their refined technique to improve our own attempts to dig through the ground. Robin Murphy of the Center for Robot-Assisted Search and Rescue at Texas A&M says:
When it comes to machines that can dig like earthworms and slip through rubble, nothing like that exists, she says. “There’s a lack of any technology short of a shovel.” Burrowing animals could inspire new machines, but so far, few studies have been able to capture the constraints robots would face in dirt-filled or muddy environments. “This is the first I’ve seen that I said, ‘Okay, we’ve got it,’” she says. [Science News]
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