When looking at the different types of sharks, you may notice that some are sleek and streamlined, like an airplane, while others are shaped like a blimp. But why is that? Jean Potvin, PhD, professor of physics at Saint Louis University, has joined researchers from around the globe logging hours by boat and in the lab in the study of hydrodynamics, his specialty. On one of his latest projects, Potvin and his colleagues at Murdoch University in Australia and the Hopkins Marine Station of Stanford University were focused on the energetics of shark swimming and its relationship to buoyancy, along with the drag force the varieties of sharks generate when they swim. Slow moving sharks are shaped more like a zeppelin, or blimp, while the faster sharks are shaped like a high-speed javelin or torpedo. Potvin and his colleagues discovered two different evolutionary paths for sharks. “The difference may be due to the drag that each kind generates,” said Potvin. In order to investigate, Potvin and the research team studied the body composition of 32 species of sharks. For the physical modeling, he used hydronamics calculations that are borrowed from aircraft performance analysis. They discovered sharks evolved attributes of aircrafts to suit their habitats.