fluid mechanics outlinealmarazr/s19-ps300/... · electric power. electric power • rate at which...
TRANSCRIPT
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FLUID MECHANICS Outline
• Density• Pressure• Buoyancy in a Liquid• Archimedes’ Principle• Pressure in a Gas• Atmospheric Pressure• Pascal’s Principle• Buoyancy in a Gas• Bernoulli’s Principle
D V
m
Density
P A
F
Pressure
STATIC AND CURRENT ELECTRICITY Outline:
• Electric Charge• Coulomb’s Law• Electric Field• Voltage Sources• Electric Potential• Electric Current• Electrical Resistance• Ohm’s Law• Electric Circuits• Electric Power
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• Magnetic Poles• Magnetic Fields• Magnetic Domains
• Electric Currents and Magnetic Fields• Magnetic Forces on Moving Charges• Electromagnetic Induction• Generators and Alternating Current• Power Production• The Transformer—Boosting or Lowering Voltage• Field Induction
Magnetism
What is electricity?•Everything is made of atoms which contain POSITIVE particles called PROTONS and NEGATIVEparticles called ELECTRONS.
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d
qqkF =
Coulomb’s law
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Conductors & Insulators
• What makes something a good conductor?
• Good conductors allow electrons to move through them easily. Insulators do not allow electrons to move easily.
insulator
Electric Potential & Resistance
Electric potential,
Voltage, V (volts)
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Conductor
Flow of electrons= current, I (Amps)
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More on Resistance
• Resistance factors– Type of material
– Length
– Cross-sectional area
– Temperature
• Superconductors– Negligible
resistance at very low temperatures
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Ohm’s Law
Ohm’s Law
relationship between current, voltage, and resistance
Current in a circuit varies in direct proportion to the potential difference (voltage) and inversely with the resistance:
current = voltage
resistance or I =
V
R
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Circuits— example problems
Electric Circuits
Devices connect to a circuit in one of two ways:
• Series • Parallel
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Electric PowerElectric power• rate at which electric energy is converted into
another form
• in equation form:
power = current voltageThe unit of power is the watts, W
Example: 100-watt lamp draws0.8 ampere
Ferromagnetism
Ferromagnetic materials are those that can become
strongly magnetized, such as iron and nickel.
These materials are made up of tiny regions called
domains; the magnetic field in each domain is in a
single direction.
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Magnetic Poles
Magnets have two
ends—poles—called
north and south.
Like poles repel; unlike poles attract.
If you cut a magnet in half — get two smaller magnets.
Magnets and Magnetic Fields
Magnetic fields can be visualized using magnetic field lines, which are always closed loops.
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Electricity and Magnetism-EMF
Switch Open: No currentAnd no magnetic field
Switch Closed: Current increases, creates and magnetic field or electromagnetic field (EMF)
Magnetic field intensity• increases as the number of
loops increase in a current-carrying coil
Electromagnetic Induction and Faraday’s Law
Michael Faraday
1791- 1867
Causes:• Relative motion between magnetic fields and conductors• Changing magnetic fields near conductors
Effect:• Induced voltages and currents
Induced voltage depends on:• Number of loops• Strength of magnetic field• Rate of magnetic field change
More loops; more induction
Faraday’s lawthe induced voltage in a coil is proportional to the number of loops, multiplied by the rate at which the magnetic field changes within those loops
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FLUID MECHANICS Outline
• Density• Pressure• Buoyancy in a Liquid• Archimedes’ Principle• Pressure in a Gas• Atmospheric Pressure• Pascal’s Principle• Buoyancy in a Gas• Bernoulli’s Principle
D V
m
Density
P A
F
Pressure
Pressure in a Liquid
• Independent of shape of container
whatever the shape of a container, pressure at any particular depth is the same
• Equation:
liquid pressure = weight density depth
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What makes water flow?
• gravity
• by placing the water up high the pressure at the bottom is high enough to supply water to all parts of town that are lower than the towerStanton, IA
Montgomery Co.
Archimedes’ Principle
Archimedes’ Principle
discovered by Greek scientist Archimedes
relates buoyancy to displaced liquid
states that an immersed body (completely or partially) is buoyed up by a force equal to the weight of the fluid it displaces applies to gases and liquids.
Archimedes of Syracuse287 BCGreek mathematician, physicist, engineer, inventor, and astronomer.
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❖ Pressure and volume are inversely related at constant temperature.
❖ PV = K
❖ As one goes up, the other goes down.
❖ P1V1 = P2V2
Boyle’s Law
Robert BoyleChemist & Natural Philosopher
Listmore, Ireland
January 25, 1627 – December 30, 1690
• Pascal’s Principle states that a change in pressure at any point in an enclosed fluid at rest is transmitted undiminished toall points in the fluid
•Applies to all fluids—gasesand liquids
Pascal’s Principle
Blaise Pascal Scientist and theologian
in the 17th century
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Pascal’s Principle• Application in hydraulic press
Example:– Pressure applied to the left piston is transmitted to
the right piston
– A 10-kg load on small piston (left) lifts a load of 500 kg on large piston (right)
Pascal’s Principle• Since the pressure in the fluid is the same at both
ends of the tube, one can cleverly change the force and area to mechanically multiply each.
• This principle underlies a lot!
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A
F
A
F
PP
=
=
1P
2
2
A
F
1
1
A
F
2P
Pn An
Fn
Pressure
n = 1, 2, 3, …
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❖ In fluid dynamics, Bernoulli's
principle states that an increase
in the speed of a fluid occurs
simultaneously with a decrease
in pressure or a decrease in the
fluid's potential energy.
Bernoulli’s Principle
Daniel BernoulliMathematician, Physicist, Inventor
Swiss
8 Feb, 1700 – March 17, 1782
Prairie dogs know how to useBernoulli's principle
Prairie dogs always have 2 entrances to their
burrows so that any difference in air speed
over the entrances produces air flow through
the tunnels.
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Applications of Bernoulli’s Principle: Torricelli,
Airplanes, Baseballs, Blood Flow
A person with
constricted arteries
will find that they
may experience a
temporary lack of
blood to the brain as
blood speeds up to get
past the constriction,
thereby reducing the
pressure.
HEAT TRANSFER AND CHANGE OF PHASEOutline
• Climate Change and the Greenhouse Effect
• Heat Transfer and Change of Phase• Boiling• Melting and Freezing• Energy and Change of Phase
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Climate Change and the Greenhouse Effect
Climate Change• Energy absorbed from the Sun• Part reradiated by Earth as longer-wavelength
terrestrial radiation
Energy Consumed Today
http://www.eia.gov/totalenergy/data/annual
Fossil fuels
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gasoline (refined oil) combustion:
2 C8H18 + 25 O2 → 16 CO2 + 18 H2O + KE
natural gas (methane) combustion:
CH4 + 2 O2 → CO2 + 2 H2O + KE
coal combustion:
C + O2 → CO2+ KE
Fossil Fuel Combustions
• CO2 is a greenhouse gas - global warming
• note that gasoline produces the most CO2 per combustion
• coal/natural gas produce less CO2 and is also cheaper BUT you don’t get as
much horsepower from coal as from gasoline – we are willing to pay more
for power
The chief oil and gas
deposits in the world
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