Answer:
A fluid is defined as a material that deforms continuously and permanently under the
application of a shearing stress.
• The pressure at a point in a fluid is independent of the orientation of the surface
passing through the point; the pressure is isotropic.
• The force due to a pressure p acting on one side of a small element of surface dA
defined by a unit normal vector n is given by −pndA.
• Pressure is transmitted through a fluid at the speed of sound.
• The units we use depend on whatever system we have chosen, and they include quantities
like feet, seconds, newtons and pascals. In contrast, a dimension is a more
abstract notion, and it is the term used to describe concepts such as mass, length and
time.
• The specific gravity (SG) of a solid or liquid is the ratio of its density to that of water
at the same temperature.
• A Newtonian fluid is one where the viscous stress is proportional to the rate of strain
(velocity gradient). The constant of proportionality is the viscosity, µ, which is a
property of the fluid, and depends on temperature.
• At the boundary between a solid and a fluid, the fluid and solid velocities are equal;
this is called the “no-slip condition.” As a consequence, for large Reynolds numbers
(>> 1), boundary layers form close to the solid boundary. In the boundary layer,
large velocity gradients are found, and so viscous effects are important.
• At the interface between two fluids, surface tension may become important. Surface
tension leads to the formation of a meniscus, drops and bubbles, and the capillary rise
observed in small tubes, because surface tension can resist pressure differences across
the interface.
