Three Properties of Pressure in a Fluid
• The forces a fluid at rest exerts on the walls of its
container, and vice versa, always act
perpendicular to the walls.
• An external pressure exerted on a fluid is
transmitted uniformly throughout the volume of
• The pressure on a small surface in a fluid is the
same regardless of the orientation of the surface.
The hydrometer is a simple
instrument based on
Archimedes’ Principle that is
used to measure the density
of a liquid.
Laminar (or streamline) flow is when every particle of fluid passing a
particular point follows the same path.
Turbulent flow is when the flow of fluid produce irregular whirls and
NOTE: The greater the speed of a fluid in stream flow, the lower the
Pressure and Speed
In a horizontal pipe the pressure is greatest
when the velocity is least, and vice versa.
The viscosity of a fluid is a kind of internal friction that
prevents neighboring layers of the fluid from sliding freely
past one another.
Viscosities of various fluids at atmospheric
pressure and indicated temperature
If the pipe is cylindrical with the length L, and
inside radius r, and a fluid viscosity η is in
laminar flow through it under the influence of
a pressure difference ∆P, the rate or flow is:
The Surface Tension of a liquid refers to the
tendency of its surface to contract to the
minimum possible area in any situation.