WHAT IS FLUID FRICTION?

FLUID FRICTION

You know that air is very light and thin. Yet it exerts a frictional force on objects moving through it. Similarly, water and other liquids exert a force of friction when objects move through them. In science, the common name of gases and liquids is fluids. So we can say that fluids exert a force of friction on objects in motion through them.

The frictional force on an object in a fluid depends on its speed with respect to the fluid. The frictional force also depends on the shape of the object and the nature of the fluid.

It is obvious that when objects move through fluids, they have to overcome friction acting on them. In this process they lose energy. Efforts are, therefore, made to minimize friction. So, objects are given special shapes. Where do you think scientists get hints for these special shapes? From nature, of course. Birds and fishes have to move about in fluids all the time. Their bodies must have evolved to shapes that would make them lose less energy in overcoming friction. You read about these shapes in Class VI. Look carefully at the of an aeroplane (Fig. 12.17). Do you find any similarity in its shape and that of a bird? In fact, all vehicles are designed to have shapes that reduce fluid friction.

The frictional force exerted by fluids is also called drag.

Figure 12.17: Similarity in shapes of an aeroplane and a bird

Source: This topic is taken from NCERT TEXTBOOK