Did you at any time wonder, why a small iron nail sinks in water, whereas a huge ship of heavy
mass floats on water? An astronaut wears a special suit while attempting to travel in space.
Why do deep sea fishes die when brought to shallow water? A submarine can move vertically
in water, i.e., it can sink in water as well as float. How does this happen? The answers to all
these questions lie in studying and understanding fluid pressure and the principles involved
therein. This branch of physics is called hydrostatics.
Matter exists in three states, namely solids, liquids and gases. Solids have a definite shape
and size, whether regular or irregular. But liquids and gases do not have a definite shape. Both
liquids and gases have a common property of ‘flowing’, and hence, are called ‘fluids’. Thus,
fluid is a substance that can flow. The interaction of fluids with its surroundings when they
are at rest, is studied in hydrostatics. In the current chapter, we deal with pressure exerted
by a fluid, transmission of pressure through a fluid and its applications, pressure exerted by
the atmosphere, the variation in atmospheric pressure and its measurement using various
instruments, bodies which are floating and immersed in fluids and the principles related
to them
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