|Class 8 Physics Friction||Fluid Friction|
Fluids (means liquids and gases) too exert friction on the objects. The frictional force exerted by fluids is called a drag. Since water and air too exert friction on the bodies that move in them like the boat, fishes (in water), aeroplane and birds, their physical structure should be such that they can oppose this friction and move forward.
Notice the similarities between the physical structure of an aeroplane (man-made) and that of an bird and also a boat(man-made) and that of a fish.