Fluids

Topic Outline
• Pressure
• Hydraulic Press
• Pressure and Depth
• Buoyancy
• Fluid Flow
• Bernoulli’s Equation
• Application of Bernoulli’s Equation
• Viscosity
• Surface Tension

Pressure
Pressure is the magnitude of the normal force
acting per unit area.

Three Types of Pressure Gages

Absolute Pressure
Absolute Pressure or the true pressure is the
sum of the gage pressure and the atmospheric
pressure.

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 fluid.

• The pressure on a small surface in a fluid is the
same regardless of the orientation of the surface.

Variation of atmospheric pressure
with height

Variation of fluid pressure with depth

Pump
Pump is a device for creating pressure difference.

Pressure and Depth
Pressure in a fluid increases with depth

Buoyancy
When the object is placed in water (or any other fluid), an
upward force acts on it. This effect, called buoyancy.

Hydrometer
The hydrometer is a simple
instrument based on
Archimedes’ Principle that is
used to measure the density
of a liquid.

Fluid Flow
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
eddies occur.

NOTE: The greater the speed of a fluid in stream flow, the lower the
pressure.

Applications of Bernoulli’s Equation
• Liquid at Rest
• Torricelli’s Theorem
• Flow from orifice

Liquid at Rest
When a liquid column is stationary, the
pressure difference between two depths is:

Torricelli’s Theorem
Torricelli’s Theorem states that the speed at
which the liquid comes out is the same as the
speed of a body falling from rest from the
height h.

Flow from Orifice
The rate at which liquid flows through the
opening is:

Pressure and Speed
In a horizontal pipe the pressure is greatest
when the velocity is least, and vice versa.

Viscosity
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

Poiseuille’s Law
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:

Surface Tension
The Surface Tension of a liquid refers to the
tendency of its surface to contract to the
minimum possible area in any situation.

Fluids

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Fluids