Transcript UNIT 2 - SharpSchool

UNIT 2
Energy Flow in Technological
Systems
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Steam Engines
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a boiler generates steam and a steam
engine converts the steam pressure into
mechanical motion
1698 Savery in England received the
first patent for a steam engine to help
remove water from mines Pg 142
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Steam Engines continued
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1712 Newcomen invented a much improved
steam engine Pg 143
1757 James Watt modified the design of the
steam engine so eventually it became useful
in many industries – Industrial Revolution
1884 Charles Parsons perfected the steamturbine engine – no pistons
steam-turbine engines still today power giant
ocean liners and cruise ships
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Scientific Theories of Heat
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1. Phlogiston Theory
substances that could burn contained
an invisible fluid – phlogiston
2. Caloric Theory
caloric or heat was a massless fluid that
was found in all substances
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Scientific Theories of Heat
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caloric could not be created nor destroyed
but could flow from one substance to another
caloric always flowed from warmer objects to
cooler objects
J Black defined a unit of caloric – the calorie
1 cal was the quantity of caloric that would
increase the temperature of 1 g of water by
1ºC
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Scientific Theories of Heat
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3. Modern Theories
Count Rumford suggested that there is
no substance such as caloric, he
believed that there was a relationship
between mechanical energy and heat
Mayer a German doctor discovered that
heat is related to energy
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Scientific Theories of Heat
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Joule a British physicist was given the
credit for discovering the mechanical
equivalent of heat
The SI unit for energy, the joule is
named in his honour
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Energy
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is the ability to do work
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Work
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is the transfer of mechanical energy
from one object to another
is a push or pull on an object that
results in motion in the direction of the
force applied
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Work
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W=FΔd
W= work in joules(J)
F= force in newtons(N)
Δd= distance in metres
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Law of Conservation of Energy
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Energy cannot be created or destroyed,
but it can be converted from one form
to another
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Calorie
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Today the calorie is defined as the
amount of energy that must be added
to 1.0 g of water to increase its
temperature by 1.0 ºC
1 cal = 4.186 J
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Heat and Thermal Energy
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kinetic energy – energy of motion
the greater the kinetic energy of a substance
the faster the particles of the substance are
moving around – kinetic molecular theory
heat is now defined as the transfer of
thermal energy from one object to another
heat and work are mechanisms by which
energy can be transferred from one object to
another
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Specific Heat Capacity
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is the amount of heat required to raise
1.0 g of a substance 1ºC
is different for every substance
symbol is ‘c’
units are ‘ J/g ºC’
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Temperature
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is a measure of the average kinetic
energy of the individual atoms or
molecules in a substance
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Thermodynamics
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is the field of physics that deals with
forces and motion involving heat(the
transfer of thermal energy)
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Thermodynamics continued
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1. First Law of Thermodynamics
Energy cannot be created or destroyed,
but can be transformed from one form
to another or transferred from one
object to another
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Thermodynamics continued
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2. Second Law of Thermodynamics
It is not possible for any process to
remove thermal energy from an energy
source and convert it entirely into work
No process can be 100 % efficient.
Some energy will always remain in the
form of thermal energy
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Thermodynamics continued
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Lost as heat
Thermal energy always flows from the
warmer object to the cooler object
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Internal Combustion Engines
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fuel is burnt inside a cylinder
the hot gases expand and push the
piston down the cylinder
modern engines have 4, 6, or 8 pistons
all attached to the same crankshaft
these pistons are designed to fire at
different times
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Internal Combustion Engines
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at least one piston is always in its’
power stroke
examine diagram Pg 165
the internal combustion engines
release greenhouse gases and gases
that contribute to smog and acid rain
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Production of Electrical Energy
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all commercial electrical energy is produced
by electrical generators
electrical generators have huge magnets
with coils of wire of wire turning between the
poles of the magnets
in most generators turbines turn the coils
kinetic energy of the coils is converted into
electrical energy
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Production of Electrical Energy
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steam pressure drives the turbines for
1/3 of the electrical energy produced in
Canada
the heat that boils the water comes
from the combustion of fossil fuels or
nuclear reactions
hydro-electric generating stations
produce 2/3 of the electrical energy
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Production of Electrical Energy
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the pressure of the water behind the
dam forces the turbines to turn
a few places in Canada are able to
make use of wind energy to produce
electrical energy
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Measuring Motion
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quantities that describe magnitude but not
direction are called scalar quantities
speed, distance and time are scalar
quantities
quantities that include direction as well as
magnitude are vector quantities
velocity, displacement and position are vector
quantities
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Distance vs Displacement
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distance is measured along the actual path
travelled
displacement is measured along a straight
line joining the initial and final positions
adding vectors head to tail allows you to
calculate displacement in two dimensions
adding vectors along a straight line allows for
calculating displacement in one dimension
(directions N,S,E,W or +/-)
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Speed vs Velocity
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both quantities involve time
time(t) is a point in time
time interval(Δt) is the difference
between two times
speed is the distance travelled by an
object during a given time interval
divided by the time interval
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Speed vs Velocity continued
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v = Δd
Δt
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velocity is the displacement of an object
during a time interval divided by the time
interval
v = Δd
Δt
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Speed vs Velocity continued
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as speed or velocity may change during
an interval of time the above formula
represent the average speed or velocity
Converting km/h to m/s
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Uniform Motion
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the velocity is constant
on a Distance-Time Graph the line is a
straight line(horizontal or slanted)
Slope = rise
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run
Slope = velocity
**When a position vs time graph is a straight
line the velocity is constant.
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Acceleration
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a change in velocity during a time
interval (speeding up or slowing down)
is a vector quantity
a force is required to change motion in
some way
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Acceleration continued
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units for acceleration are m/s2
(5m/s2 means the speed is changing at
5m/s every second)
formula is a= ∆v
t
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∆v= change in speed
t = time in seconds
a = acceleration (m/s2)
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Acceleration continued
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∆v = vf - vi
vf = final speed (m/s)
vi = initial speed (m/s)
a = vf - vi
t
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Graphing Accelerated
Motion
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a position time graph for acceleration is
a curved line as the speed is changing
when speed increases the graph
curves upward
when spedd decreases the graph
curves downward
a velocity time graph of uniform
acceleration is a slanted line.
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Kinetic Energy
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is the energy of motion
the amount of KE an object has
depends upon its speed and its mass
KE or Ek = 1/2mv2 or mv2
2
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Kinetic Energy
continued
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Ek = kinetic energy in joules (J)
m = mass of the object in kilograms(kg)
v = speed in metres per second (m/s)
1 J = 1 kg m2
s2
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Potential Energy
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is the stored energy
it has the potential to do work
many forms of PE
eg. elastic, chemical, nuclear, electrical
and gravitational
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Gravitational Potential
Energy
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is the energy an object has due to its
position above the earth’s surface or
some other point of reference (a table)
for an object to posses Peg work must
be done on it
Thus ‘work and energy’ are equivalent
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Potential Energy continued
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PE or Ep = mgh
m = mass in kg
g = 9.81 m/s2
h = height in m
PE = potential energy (J)
W = Fd
= Fgd
= mgh
h=?
m=?
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Weight
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***Weight is a force
Fg = mg
units for weight are N (kg m/s2)
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Efficiency of Energy
Conversions
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Efficiency
is a measurement of how effectively a
machine converts energy input into
useful energy output
the energy that perform the task is
called useful energy
some energy is always lost – usually as
heat
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Efficiency of Energy
Conversions
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efficiency = useful output energy x 100%
total input energy
Second Law of Thermodynamics
“No process can be 100 percent efficient.
Some energy will always remain in the form
of thermal energy”(wasted energy)
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Energy Efficiency and the
Environment
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every time there is an energy
conversion some energy is wasted in
the form of heat
example – hydro-electric generating
stations are 70% efficient while coal
burning stations are 35% efficient
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Energy Efficiency and the
Environment
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businesses and industry are the largest
consumers of energy and so it is
important that they use energy
efficiently
many companies have already installed
more energy efficient lighting, heating
and cooling equipment to conserve
energy
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Energy Efficiency and the
Environment
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all sectors of society must become
conscious of the problems and search
for solutions
the solutions must be sustainable
a sustainable process will not
compromise the survival of living things
or future generations while still
providing for our current needs
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Energy Efficiency and the
Environment
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another less obvious method is to encourage
industries to use cogeneration
cogeneration is the process of using waste
energy from one process to power a second
process
eg. in a thermal power station, the steam
that is used to turn the turbines could then
be used to heat local buildings
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