5. DRAG
lPressure drag: Resistance by water preventing forward motion.
lFrictional drag: Friction due to rubbing of fish body against water molecules.
lVortex drag: Pull upon lift.
7. SUBMARINE
lIt works on Archimedes principle of buoyancy.
lIt operates using negative buoyant force by displacing less
l water than its weight or by increasing its own weight.
l
8. SWIM BLADDER V/S BALLAST TANK
lA Ballast tank is replacement of swim bladders in a submarine.
lWhile fishes only control the volume of air in their bladder,
lthey do not displace water unlike submarines.
9. CONTD.,
lThe ballast tank fills itself with pressurised air upon rising and
l with non-buoyant water upon sinking.
lAt a certain depth they maintain their position by neutralising
lbuoyant force.
11. HYDRODYNAMIC DRAG
lThe Cigar shape of the submarine help to reduce this drag.
lHydroplanes control angle of lift and dive to counter Vortex
l and Pressure drag..