UNIT 2 - MECHANICS
CHAPTER 8 - FLUID MECHANICS
Chapter 8A – Properties of Fluids
• Objectives:
– Identify what is studied in fluid mechanics
– Define pressure
– Show how different physical properties affect
pressure
– Calculate pressure when given applied force
and area
– Recognize units of pressure
– Discuss the factors affecting fluid pressure in
natural and manmade settings
– Describe how instruments measure pressure
– State Archimedes’ principle in your own words
– Calculate specific gravity
• Assignment: Section Review, page 181
Fluid Mechanics
• The study of how fluids flow and how forces
and energy are transmitted through fluids
• Divided into two parts
– Hydrostatics
• The scientific study of fluids, especially noncompressible liquids, in equilibrium with their
surroundings and hence at rest
– Hydrodynamics
• The scientific study of the motion of fluids, especially
non-compressible liquids, under the influence of
internal and external forces
• Fluids
– Matter that assumes the shape of their
containers
– Both liquids and gases are fluids
Pressure
• The force exerted perpendicularly on a unit
of area
• Units are Pascals (N/m2)
• Formula
• P=F/A
• P=pressure
F=force
A=total surface area
• Larger area = lower pressure
Fluid Pressure
• A property of all fluids in which pressure
is exerted equally in all directions at any
point in the fluid
• Exists because liquid and gas particles
are not held rigidly in place
• Kinetic theory??
Factors Affecting Fluid Pressure
• Let’s Read page 176
• Gravity and fluid properties
– Fluid’s have weight
– Pressure is not affected by the volume or
shape of the container
– Fluid density
• Hydrostatic pressure
– Water pressure due only to depth in a body
of water
Pressure Instruments
• Evangelista Torricelli
– Served as Galileo’s secretary
– Created the first true vacuum and invented the
mercury barometer
• An instrument that measures atmospheric pressure and
consists of a column of mercury in a sealed glass tube
containing a vacuum
• Aneroid barometer
– An instrument for measuring atmospheric pressure
that consists of a sealed flexible can that expands
and contracts with changes in air pressure
• Gauges
– A mechanical device connected to a fluid system
designed to indicate gas or liquid pressure
– Bourdon Tube
Buoyancy
• Let’s Read page 179, section 8.4
• Archimedes’ principle
– States that the buoyant force exerted by a
fluid on an immersed object is equal to the
weight of the fluid the object displaces
• Buoyant force
– A lifting force exerted by a fluid on an
immersed object
• Positively buoyant – objects that float
• Negatively buoyant – objects that sink
• Neutrally buoyant – do not rise or sink
Specific Gravity
• The ratio of a substance’s density to
water’s density
• A unitless quantity numerically equal to
the density of the substance
• Also called relative density
• Let’s Read page 181
Chapter 8B – Hydraulics & Fluid Flow
• Objectives:
– State Pascal’s principle and discuss the
conditions under which it applies
– Describe a simple hydraulic machine and how it
relates to other simple machines
– Discuss the causes of fluid flow and explain
how they apply in familiar examples
– Summarize Bernoulli’s principle and identify the
three quantities whose sum must be conserved
in a closed fluid system
– List the characteristics of two principal kinds of
fluid systems that obey Bernoulli’s principle
– Describe the Coanda effect and explain how it
is responsible for exerting forces in fluids
• Assignment: Section Review, page 188
Pascal’s Principle
• Let’s Read page 182, section 8.6 & 8.7
• States that changes of pressure on the
surface of a confined fluid are exerted
equally throughout the fluid and at all points
on the fluids’ container
• Hydraulic machine
– A liquid filled machine that uses Pascal’s
principle to convert a small force exerted on a
small diameter piston to a large force exerted
by a large diameter piston to do work
• Hydraulics
– The area of physics that deals with the transfer
of forces and work done by confined fluids
according to Pascal’s principle
Flowing Fluids
• How does water get from the pipes to
your sink?
• How does a vacuum work?
• What about when you breathe?
• Let’s Read page 183, section 8.8
Bernoulli’s Principle
• States that total energy (represented by
kinetic energy, potential energy, and
pressure) for a confined ideal fluid
flowing through a pipe is conserved at all
locations within the pipe
• Let’s Read page 185, section 8.9
• Venturi
– A specially designed constriction in a pipe,
used to measure fluid flow rate by
comparing the differences in fluid pressure
before and within the constriction that occur
according to Bernoulli’s principle
Coanda Effect
• The tendency of a fluid flowing past a
curved surface to follow the surface
• Let’s Read page 186, section 8.10
• Lift
– The supporting force on an air foil or
hydrofoil created as it moves through a fluid
• Air foil
– A streamlined shape designed to produce
life as it moves through the air or as air
moves past it
• Facet, page 187
Chapter 8C – Gas Laws
• Objectives:
– Summarize the history of the discovery of
the gas laws
– State Boyle’s law
– Show how Boyle’s law is predicted by the
particle theory of matter
– Perform calculations using Boyle’s law
– State Charles’s law
– Show how Charles’s law is predicted by the
particle theory
– Perform calculations using Charles’s law
• Assignment: Section Review, page 194
Lots of Scientists in this Chapter!!
• So Far…
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Blaise Pascal
Evangelista Torricelli
Eugene Bourdon
Archimedes
Daniel Bernoulli
Henri Marie Coanda
• Coming Up…
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Guillaume Amontons
John Dalton
Joseph Gay-Lussac
Amedeo Avogadro
Robert Boyle
Jacques Charles
Extra Credit????
Boyle’s Law
• States that the volume of a fixed quantity
of a confined gas is inversely
proportional to its pressure when its
temperature is held constant
• Formula:
– P1V1=P2V2
– P=pressure V=volume
• Example Problem 8-1 & 8-2
• How is this useful??
– Compressed air?
Charles’s Law
• States that the volume of a fixed quantity
of a confined gas is directly proportional
to its absolute temperature when its
pressure is held constant
• Formula:
– V1/T1 = V2/T2
– V=volume T=temperature in Kelvin!
• How do we get Kelvin from Celsius??
• Example Problem 8-3
• Facet, page 195
TOMORROW!!
• Vocabulary Quiz
– Includes all vocabulary throughout the
entire chapter, PowerPoints, and
board; not just the box at the end.
• Complete Chapter Review in Class
• Study for Chapter 8 Test