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Physics Colloquium
Friday, Mar. 21th, 2008, 4:00 P.M.

E300 Math/Science Center; Refreshments at 3:30 P.M. in Room E200

Daniel I. Goldman

School of Physics and School of Biology
Georgia Institute of Technology

Locomotion on controlled granular media

Organisms like insects, lizards and crabs negotiate complex terrain in ways that no human-made robot can. While there has been progress made in the study of terrestrial locomotion on rigid, level, high friction substrates, understanding how organisms move over materials that present a complex foot interaction (like sand, bark, leaves, grass) is still a challenge since the physics of interaction of with such materials is largely unknown. We discuss laboratory experiments and numerical simulations of locomotion of biological organisms and robots on and within an example of a complex terrestrial substrate, a granular medium. We control the packing fraction and material strength of the granular medium by use of a trackway composed of a fluidized bed. We study how the fluidizing properties of granular media affect speed in rapidly running and swimming lizards. We compare our biological results to systematic studies of a physical model of an organism, a 2 kg robot SandBot. To understand the physics of interaction with the substrate, we measure forces during impact and drag of simple objects and compare these to soft-sphere Molecular Dynamics (MD) simulations. We simulate the robot locomotion by using the MD code to compute ground reaction forces on the limbs of a numerical model of the robot.

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