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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)

e-e-e-e-

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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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I

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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