Transcript Physics Perspectives of Environments

Physics perspective
of environment
What is energy?
Work (Moving an object)
 An object in motion
 Field with an object (e.g. An object put at

higher place)
Heat
 Light
Etc.
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Making energy
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Making heat by burning oils or coals, etc.
Utilizing steam or combustion to create a
physical force
Using the force to create electricity
Utilizing motions in nature to create electricity
Using chemical reactions to create electricity
Utilizing quantum reactions to create electricity
Using nuclear reactions to create heat
Engine system
Intake air and vaporized fuel
2. Compress the air-fuel mixture
3. Ignite the gas
4. Exhaust fumes
To be repeated
1.
Energy cycle system
(General concept of engine)
Energy as a
different form
Fuel
(Energy sources)
Work / Motion
Intake
Exhaust
Rotating turbines / crankshaft, etc.
Ecology and energy circulation
Fuel
(Energy
sources)
Fuel
(Energy
sources)
Work /
Motion
Work /
Motion
Bio-system B
Bio-system A
Fuel
(Energy
sources)
Work /
Motion
Bio-system C
Introduction to thermodynamics
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The zeroth law
 Thermal
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The first law
 Energy
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equilibrium and principle of thermometer
conservation
The second law
 Entropy
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The third law
 Infinite
processes to reach absolute zero degree
Zeroth law of thermodynamics
Systems A and B are thermal equilibrium
with system C.
 Namely, A and B are equilibrium with each
other.
 This process defines temperature.
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Thermal equilibrium
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Thermal equilibrium is not uniformity of heat,
but there is not heat flows between systems.
40
degrees
80
degrees
The heat flows from higher
to lower temperatures.
60
degrees
60
degrees
The heat flow is diminished and
the temperature is stabilized:
Thermal equilibrium
Latent heat 1
When a substance transforms into a
different phase, the heat flows between
the phases without change of the
temperature.
 The heat that plays this role is known as
latent heat.
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Latent heat 2
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When ice melts, the heat is absorbed by
80 cal per gram.
 That
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is why ice can keep things refrigerated.
When water is vaporized, the heat radiates
540 cal per gram.
 When
sweat dries out, the surface of your skin
is significantly cooled down.
First law of thermodynamics
The internal energy of a
system transforms into
heat flows.
 As a system, the internal
energy and heat flow are
conserved.

Q2
Q1
|QT – Q1| = |Q2 – QT|
QT
Second law of thermodynamics
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In an isolated system, the entropy cannot
decrease.
 Energy
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and substances are diffused.
The work done by heat cannot generate the
same amount of internal energy.
Entropy 1
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Entropy id defined as the
change of the heat energy
divided by the absolute
temperature.
The process of heat flow
entails the increase of
entropy
The entropy after the heat
flow is larger.
Q
S 
T
Q2
T2
<
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40
degrees
T2
Q1
T1
80
degrees
<
T1
Entropy 2
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When vapor becomes water
by cooling, it looks like the
entropy decreases.
This is because it is an open
system. In terms of the
larger system, the entropy
increases by the heat
radiation.
radiation
absorption
Water
Vapor
Third law of thermodynamics
As the temperature approaches zero, the
entropy also approaches zero at
thermodynamic equilibrium.
 In principle, it is impossible to reach
absolute zero.
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Steam engines
This was started from the transformation
of energy sources. [Wood  Coal]
 People needed innovation of technology to
utilize coals effectively.
 T. Savery, T. Newcomen, and J. Watt
developed steam engines with energy
from coals. [The end of 17 to the middle of 18
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centuries]
Newcomen’s engine
1.
2.
3.
4.
5.
Burn the coals.
Boil the water.
The steam raise the
pressure of the cylinder to lift
the piston.
Feed water into the cylinder.
Then it pulls down the piston
by lowering pressure.
piston
cylinder
Water
feeding
drainage
water
Watt’s engine
2.
3.
4.
5.
Burn the coals.
Boil the water.
The steam raise the
pressure of the cylinder to
lift the piston.
The steam goes down into
the condenser and it is
cooled down to become
water.
Then it pulls down the
piston by lowering pressure.
piston
cylinder
condenser
1.
cooling water
water
Work and energy
Work = force  distance
 Kinetic energy = 1/2massspeed2
 Gravitational potential energy =
massgrav.accel.height
You can find other energy, such as wind,
water flows, chemical reactions, etc.
These are exchangeable each other.
Energy  Work
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First law of thermodynamics
revisited (Energy conservation)
In a system, sum of all the work and
energy is constant.
 They compensate each other; for example,
more force with less distance, and less
force with more distance to move an
object.
 Without having energy from outside, the
system cannot continue to work.
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Entropy and work
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Entropy increases at the direction of
the thermal processes.
Work capability can be associated with
the entropy.
Energy /
substances as a
different form
Energy
sources
Work / Motion
Intake
Lower
entropy
Large capability
to work
Exhaust
Increasing
entropy
Higher
entropy
Small capability
to work
Heat as energy
The heat created from electricity is: Q=RI2t
where Q, R, I and t are heat, resistance,
current and time.
 Heat itself is energy: E = kT where k and T
are Boltzmann const. and temperature.
 1 calorie = 4.19 joules
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Carnot cycle 1
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The low grade
heat source
plays an
important role.
All the given
heat cannot be
used only for
the work
because the
engine is
stopped.
Part of the
given heat is
absorbed into
the law grade
heat source.
The heat source gives
heat to engine.
High grade heat source
The inside engine is
expanded.
The internal energy
flows into the lower
heat source.
Low grade heat source
The inside engine
shrinks.
Carnot cycle 2
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This is a reversible
system. (repeatable)
The efficiency is given
only by T0 and T1.
This system includes
the direction of the
heat flow.
High grade heat
Thermal system
Low grade heat
T1
T0
Work
T1  T0
efficiency 
T1
Human-activity system as an
engine
*Petroleum
*Natural gas
*Residue
*Metals
*Work / Motion
*Exhaust gas
*Chemical
*Products
*Contaminated
*Water
*Electricity
water
Intake
Exhaust
*Other
substances
Excess of each process may cause problems…
Depletion of
natural resources
Destroying ecology
Waste disposal
problems
Pollutions
Destroying ecology
Human activity and environmental
structure
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Natural resources will be depleted when human
consumption is more than the quantity that
nature can produce.
Other biological systems play very important
roles to keep various equilibria on the earth.
Environments need to have margins to
neutralize exhausted products to manage entire
ecology.
Water as an important factor in
environment 1
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Water is harder to be heated up and
harder to be cooled down. (= high specific
heat: 4186 J/kg K)
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This provides a stable environment on the
earth.
Water as an important factor in
environment 2
Rain fall as
cooled down
vapor
Water
vaporization
The vaporized water
becomes lighter to go
up. Then, it gets cooled
there and falls as rain or
snow.
Due to the latent heat and
radiation, this process
Remove excess heat from
the earth.
Heat radiation
Bio-system and its cycle
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The system is based upon sun shine and water.
Plants produce carbohydrates (sugars) to feed
animals.
Animals’ excretory substances are degraded by
bacteria.
The substances degraded by bacteria are used
for plants.
This process repeats.
Heat death of the universe 1
If the entropy keeps on increasing, every
system will become equilibrium, which is
called heat death.
 However, an open system exchanges
lower and higher entropies.
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Entropy keeps increasing in a closed system.
Heat death of the universe 2
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In the universe, the entropies flow as in the
structure:
Universe
The direction
of lower
entropies
Environmental
activities
(engines)
The direction
of higher
entropies
Ecological systems 1
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Biological creatures inhabit 10 km (6.21
miles) from the surface of the earth.
Plants produce carbohydrates by
photosynthesis.
Animals consume them and excrete as in a
different substances.
Bacteria and fungi biodegrade the
substances and carcasses for plants.
Ecological systems 2
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Bacteria play an important role for the cycle.
especially for the circulation of nitrate
Bacteria
(biodegrading
detritus)
Animals
(consuming
plants and other
animals)
Detritus
(carcasses
and dead
leaves, etc.)
Organic substances
Inorganic
substances
Plants
(producing
carbohydrates
and proteins)
Ecological systems 3
Bacteria biodegrade carbons and nitrides
in detritus into CO2 (carbon dioxide), NH4+
(ammonium ion), and NO3- (nitrate ion).
 Amount of CO2 crated by bacteria is
exactly the same amount consumed by
plants.
 One gram of soil contains about 1 billion of
bacteria (1 million kinds).*
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* Computational improvements reveal great bacterial diversity and high metal toxicity
in soil. J. Gans, et al. Science, 309, 1387-1390 (2005)
Photosynthesis 1
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A simple
description of
photosynthesis:
O2
Sun light
CH 2 O
CH2O is the product
from photosynthesis.
Breathing:
CH2O + O2  CO2 + H2O
CO2
Photosynthesis:
CO2 + H2O  CH2O + O2
Water
Inorganic
substances
Insects fungi
bacteria
Photosynthesis 2
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The carbohydrate produced by
photosynthesis is glucose, C6H12O6.
6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O
Many of glucose get bonded to become
starch.
 Starch is multiple glucose missing water:
(C6H10O5)n
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Photosynthesis 3
The entropy of carbon atoms seems
decreased by photosynthesis, but the
entropy of the larger system is surely
increasing.
How?
 Remember that vaporization of water
makes the entropy increased.
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Photosynthesis 4
The actual chemical reaction of
photosynthesis is:
6CO2+6H2O+6H2O  C6H12O6+6O2+6H2O
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for photosynthesis
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liquid
vapor
The H2O of right hand side radiates heat
due to the latent heat. (The increase of
entropy)
Entropy and photosynthesis
To produce glucose by photosynthesis, it
needs sufficient water not only for the
chemical reaction but also for the “exit” of
entropy.
 It is said that the imbalance of the entropycirculation system may cause
desertification or other malfunctioning of
plant systems.
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Water on the earth 1
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Specific gravity (S.G.)
 In
general, most of S.G. of substances become
larger (i.e. heavier) when they are refrigerated,
but water is different.
 Water has S.G., 1.0 when it is at 4 degrees of
Celsius. (the heaviest)
 Temperature of water, Tw. Tw=0  S.G.=0.999;
Tw=50  S.G.=0.988; Tw=100  S.G.=0.958.
 The S.G. of ice is 0.917.
Water on the earth 2
The S.G. of water does not depend on the
temperatures significantly.
 The S.G. of ice is smaller than the liquid
phase of water; therefore, the ice can float.
 This makes water circulate faster and
more easily; thus, it has generated variety
of biological species.
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