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L14-15_Swimming_F09_HANDOUT - swimming page 1 EEMB 106 FISH...

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swimming, page 1 EEMB 106, FISH: HOW FISH SWIM I. Themes : 1) How the basic vertebrate system is adapted to moving through water. 2) Introduction to the osteology and musculature system of fishes. 3) The amazing diversity of design features (for swimming) that are expressed by fish. No trivial task; i) Water is 800 times denser than air, ii) 50 times more viscous than air iii) far lower [O 2 ] for respiration. Therefore, must be extremely efficient (movement/energy expended). Primary purpose of movement is to feed or avoid being eaten. Very strong selective force. So, system has evolved to: a) minimize energy requirements b) increase acceleration and speed c) improve manueverability d) compromise between and fine tuning of a,b, and c. II. Mechanics of moving through water: (hydrodynamics) Motion is a balance between two hydrodynamic forces; those that resist and those that generate propulsion: Resistance = inertia + drag Inertia = energy required to start something in motion Drag = force that acts backwards along the direction of motion; comprised of 2 components i) friction drag - ‘stickiness’ of water along side. Caused by H 2 O molecules bouncing off fish (given forward velocity). Proportional to velocity of water or fish and body surface area . boundary layer = thin layer with steep velocity gradient ii) pressure drag - caused by distortions of flow around fish’s body. Net pressure difference between head (high pressure) and tail (low pressure). Proportional to velocity and body shape . Fish evolved to simultaneously reduce resistance (all components of drag) and generate propulsion. Pike Tuna Perch turbulent wake flow separation
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swimming, page 2 Ways to minimize drag: i) fusiform body shape (streamlining) reduces pressure drag ii) mucous/slime reduces friction (evidence inconclusive) iii) fins tuck into folds in body ) iv) vortex generators placoid and ctenoid scales may have evoloved independently in sharks and teleosts, respectively to retard separation of the boundary layer. Small vortices prevent larger ones and help stabilize the boundary layer. Two forces that enhance propulsion: lift and thrust. Lift - force perpendicular to direction of motion. Keeps moving object aloft in the water column. When water moves faster over one surface than another.
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L14-15_Swimming_F09_HANDOUT - swimming page 1 EEMB 106 FISH...

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