Slime reduces friction

Press, Volume CXI, Issue 32798, 24 December 1971, Page 11

Slime reduces friction

that the shape of the object going through the water is suitably smooth and streamlined, is to prevent a turbulent flow of water around the object There are two distinct kinds of flow in fluids: laminar and turbulent. In laminar flow the fluid moves smoothly, in parallel layers and at even rates of speed, past the object In a slow-moving stream with no obstructions the flow tends to be laminar. In turbulent flow the fluid moves with varying pressures and speeds past the object. These eddying movements exert far more friction on such a surface than laminar flow and slow the progress of tfie object.

Slime exuded A fish, searching for food, swims so slowly that he generates little or no turbulence. But when he darts to escape a predator or to catch his prey, his speed is. limited by , turbulence generated along his body. ' It now appears that swiftly moving fish like the barracuda and halibut exude a slime that acts as a highly efficient reducer of turbulence. The slime doe? not dissolve in water except in the presence• of turbulence. Thus the fish swims casually about with its slimy coating intact until it needs a burst of speed. As soon as it chums up water in its dash, turbulence dissolves the top layer of slime, which then subdues the turbulence by changing the property of the water so that it flows in a laminar manner. Succeeding layers of slime make the process continuous. Fish slimes are also believed to

serve other functions, such as offering protection from bacterial infection and lubrication of scales. - The study was carried out at the Naval Undersea Research and Development Centre m Pasadena, California by Moe W. Rosen and his assistant, Neri E. Comford, It was described in thb British journal '"Nature,!’ and more recently by Mr Rosen in an interview. ‘

Fresh and salt Both ocean and fresh water fish carry the highspeed slime, though not all species do so. In the fresn water fish studied it was found that the small mouth bass, various forms of'trout and other species .all carry slime .that in sufficient , concentration reduces friction by close to 60 per cent.' In the ocean. Pacific are the best equipped, with the California halibut a. close second. ~ The manner in which the slime on fish like the barracuda dissolves away in moments of, crisis .. .is reminiscent of re-entry Into the earth’s atmosphere from space flight The nose cone of a missile.or spacecraft ft coated with material, that as it becomes hot breaks away, carrying the heat with it Would it be possible to coat hulls with material that di? solves away at times when high speed? are called for? Orwould it be possible to do nature one better with i coating that substantially reduces friction while remaining intact? This is ag area of research that is sure to receive renewed attention. —Copyright “New YorJ* Times” news service.