What is fluid friction? What are the factors on which it depends? Why do birds and fishes have streamlined shape?

Explanation

The frictional force exerted by liquids and gases is called fluid friction. It depends on the speed of object with respect to the fluid. It also depends on the shape of the object and nature of the fluid.
When objects move through fluids they have to overcome friction acting on them. In this process they lose energy. Since birds and fishes have to move about in fluids all the time. To reduce friction their bodies have streamlined shape so that they lose less energy in overcoming friction.