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Introduction
A fluid is a substance which cannot preserve its own shape..
A fluid is a material substance which cannot sustain a shearing stress when it is at rest.
A fluid can be either a liquid or a gas. A liquid retains a set volume and has a surface of separation above which is
a vapour and below which is a liquid. A gas, whatever its quantity, when
placed in an empty closed vessel will fill the vessel completely. It is important to note
that a gas is generally considered to be an compressible fluid and a liquid is generally considered
to be incompressible. In practice a liquid is compressible but generally very large pressures are
required to cause quite small changes of volume.
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