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13 de jul. de 2022
In Discussões Gerais
Written by Amy Lang and Translated by Lim Ji-gyun By turning up their scales, sharks can suppress eddies in the wake around them, reducing drag while swimming. The mako shark swims very fast in the sea, and some studies estimate that its swimming speed can be as high as 100 kilometers per hour, which is called the cheetah in the sea. Being able to swim so fast doesn't just depend on strong muscles and streamlined looks. All sharks are equipped with enamel-covered scales that resemble many small translucent teeth called dermatodonts. Fast-swimming sharks, such as the mako, have small skin teeth, about 0.2 cm (see Figure 1). These tough scales not only play a photo background removing protective role, but also play an important role in the hydrodynamics of the shark's swimming. friction and pressure There are two main types of resistance that sharks experience when swimming: the first is the resistance from the viscosity of seawater. From the shark's point of view, the water around it will stick to the surface of its scales, which is the inefficiency in fluid mechanics. Slip condition (no-slip condition). This phenomenon causes a layer of seawater (that is, the boundary layer) around the shark's body to be affected by viscosity, and the flow rate is different from that of the overall seawater. Outside the boundary layer, the seawater flow velocity can be regarded as a constant value. 2dd43b093b7b594c021aea4a549775ae Image credit: Physics Today Figure 1. Dermal teeth on the body surface of the mako shark. The red areas indicate the raised or flared parts of the denticles, which are 30 degrees on the fins and up to 50 degrees on the flanks. Electron microscopy captures different morphologies of the denticles on the flank, including: flat (panel a), erect (the background dentures are not erected, panel b), and the denticles are aligned in the direction of the water flow grooves (panel c). (Large image: Lukas Walter, shutterstock.com. Three small images: Philip M
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