Gray's paradox

The Graysche paradox is a flow effect, which, as the dolphins occurs during rapid whales. The body, especially those species has in reality more than much better flow properties, than this is the case with a technical body of the same shape. The name goes back to the British zoologist James Gray. He had suspected, the muscles of these marine animals is not powerful enough to maintain the observed swimming speeds of ten meters per second against the resistance of the water.

This phenomenon is attributed to the absorption characteristics of the skin, which attenuates annoying vortex formation. To this end, the dermis has ( corium or dermis) long papillae, which form a seam and are intertwined with the overlying epidermis. The papillae of the dermis are seated on lamellae, which are largely transverse to the longitudinal body axis and thus also provided to the flow direction. Due to its length keeping the papillae first for excretory ducts of sweat glands, today it is known, however, in addition to the real function of the structure and that whales do not possess skin glands, with the exception of the mammary glands. In addition to these structures, the attenuation skin has a microscopically fine relief pattern and by the results of physiological experiments also an active reaction of the skin is assumed.

The improvement of the flow properties could be adjusted by various experiments with artificial whale skin.

Resolution of the paradox

Frank Fish of the University of Pennsylvania and Tim Wei of Rensselaer 's School of Engineering in the State of New York in 2008 solved the paradox. They filmed two bottlenose dolphins while swimming. The movements of hundreds of thousands of tiny air bubbles in the water were recorded on video and analyzed by computer. So could the force to develop the dolphins with their tail fin are measured: on average more than 940 newtons. Hence, the force, which the animals can reach for the propulsion normally, about ten times greater than James 1936 Gray suspected. Is a dolphin upright on his fin above the water surface, the force of up to 1800 Newton is even up to 20 times higher than that assumed long. The results were presented in San Antonio, Texas, on a physicist Congress. Quote: "We can now say that we have solved the mystery. The answer is quite simple: The dolphins are much stronger than James Gray and many other people thought. "

Swell

• Paradox
• Zoology