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UNIT 2 - MECHANICS

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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 non-compressible 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

- Hydrostatics
- 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=pressureF=forceA=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…
- Blaise Pascal
- Evangelista Torricelli
- Eugene Bourdon
- Archimedes
- Daniel Bernoulli
- Henri Marie Coanda

- Coming Up…
- 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=pressureV=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=volumeT=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