How do sharks reduce drag? And what are the engineering applications? There are three types of drag present on the shark during locomotion. The first type of drag is known as frictional drag, which is the greatest element of drags in the shark. This is arises due to the friction created between the skin and the boundary layer and can be reduced with a condition that the boundary layer maintains a turbulent flow. The second type of drag is pressure drag, which causes by water deflecting off the moving body of a shark and can be minimise if the boundary layer remains stable and in contact with the body along its entire length. The last type of drag is induced drag. This drag is results from the turbulence of the vortices formed along and behind the posterior edges of fins, causing a wake. The wake is formed from the pressure difference between the pressure drag and frictional drag as the boundary layer separates from the body of the shark and interacts with the outer water layer.  Despite the fact that drags can resist a motion of a moving object, shark is still able to swim at a high speed. The reason is because dermal denticles on the shark skin are ribbed with longitudinal grooves which result in water moving more efficiently over their surface. Over the smooth surfaces, fast-moving water begins to break up into eddies, in part because the water flowing at the surface of an object moves slower than water flowing further away from the object. The difference in water speed causes the faster water to get “tripped up” by the adjacent layer of slower water flowing around an object. To reduce the formation of eddy, the grooves in a shark’s scale play an important role. The grooves will reinforce the direction of water flow by channelling it, so they speed up the slower water at the shark’s surface, which lead to the reduction in the difference in speed of surface flow and water just beyond the shark’s surface. On the other hand, the grooves pull the fast moving...
References: http://www.bio.davidson.edu/Courses/anphys/2000/Tuscano/Tuscano.htm [27th November 2012]
 Ask Nature, A Project of The Biomimicry 3.8 Institute (2011), Skin Reduces Drag: Shark [Online], Available:
http://www.asknature.org/strategy/038caf2e453c09b3016465cc6ca93605 [27th November 2012]
 NASA (1993), NASA Riblets for Stars & Stripes [Online], Available:
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