Mysteriously Speedy Dolphins: Gray’s Paradox Solved

Remember Gray’s paradox? In 1936 the eponymous British zoologist James Gray couldn’t reconcile his observations of dolphins swimming at speeds of over 20 miles per hour with his calculations, which demonstrated that dolphin muscles simply weren’t built to produce enough acceleration to overcome drag. He ended up blaming this drag violation on dolphin’s skin, postulating that it must have drag-reducing properties.

Fast forward decades later to this year’s Annual Meeting of the American Physical Society (APS) Division of Fluid Dynamics in San Antonio, Texas, where professor Timothy Wei of Rensselaer School of Engineering announced that he and a team of researchers had solved Gray’s paradox- and no, skin has nothing to do with the speediness of these adorable sea mammals.

Wei and his team are the first to provide solid evidence illustrating that dolphins actually do produce enough force to overcome drag. “The scientific community has known this for a while, but this is the first time anyone has been able to actually quantitatively measure the force and say, for certain, the paradox is solved, said Wei in a Rensselaer Polytechnic Institute press release.

Using combined force measurement tools developed for aerospace research with Digital Particle Image Velocimetry (a video-based measurement technique that captures 1,000 video frames per second), Wei tracked two bottlenose dolphins, Primo and Pula, as they swam through water heavily populated with tiny air bubbles.

The color-coded results showed the speed and direction of water flow around and behind the each dolphin, enabling the researchers o calculate precisely how much force was produced.

Turns out they produce way more force that Gray ever imagined- approximately 200 pounds of force is created by tail flapping ( in contrast, Olympic swimmers only generate 60-70 pounds of force at top speed). Good thing dolphins are considered harmless!

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