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LOCOMOTION/BIOMECHANICS Locomotion Adaptations (4): Swimming Terrestrial limbless locomotion Flying Terrestrial limbed locomotion SWIMMING: Axial/Appendicular skeletons propulsion under or upon water o Fish – swim using body and caudal fin, medial dorsal fin and/or anal fins or paired pectoral and pelvic funs Primary swimmers vs. secondary swimmers o Evolved directly from aquatic ancestors or moved to aquatic from terrestrial habitat Swimming actions o Undulatory mechanisms = waves passed along body/fin Long-bodied Ex. eels, sea snakes o Oscillatory mechanisms = beating paired appendages back/forth, up/down Paddle, bird wing Guidelines (10): o 1. Reduce resistance of water to motions of moving body o 2. Propel themselves in relatively dense medium o 3. Control vertical position in water o 4. Maintain orientation and steer body Secondary swimmers must exclude water from respiratory passages/ears o 6. Avoid harm from compression pf gas-filled spaces o 7. Alter ears and eyes to function under water o 8. Modify circulatory and respiratory physiology to permit suspension of breathing, avoid getting the bends o 9. Deal with thermo regulation in an environment with high thermal conductivity o 10. Adapt reproductive biology to life in water Drag = resistance that a medium offers to the motion of the object o Film of water surrounds moving object in water, wets its surface, and moves with it – short distance water isn’t moving with object gradient of moving water between water and moving object declining from the speed of the object at the object’s surface to speed of surrounding undisturbed water = Boundary Layer (thicker towards moving object’s posterior end)
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Frictional drag = moving object slowed down by shearing forces of boundary layer Smooth, streamlined object moves slowly through water successive layer (lamina of boundary layer) move slip past without eddies = Laminar flow Object accelerates boundary layer increases thickness roughness to surface = eddies o Energy from moving object, increasing drag = Turbulent flow o Object displaces volume of water 1/3 object’s volume suction, water backfills in = Pressure Drag o Friction + Pressure Profile Drag = shape object presents to moving fluid Change in profile = change in drag Pressure drag low when body long, slender Friction minimalized with short and pump morphology – decrease in surface area relative to volume o Optimal body shape = streamlined, circular in cross-section, thickest near center length (diameter 1/4 -1/5 length tuna, swordfish, and dolphins Adaptive features: o Eliminate projections (produce eddies/increase drag) o Lose external ears, testis further back in abdomen o Limbs shortened, positioned close to body (decrease frictional resistance) o Increase laminar flow – fishes evolved smooth scales or slime (reduces water viscosity), long tail fins = streamlined
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