Physics 105 Fall 2011
Physics for Decision Makers:
The Global Energy Crisis
Lecture 17 Midterm Review
The midterm exam
 Next Tuesday
 You are allowed one side 8 1/2” x 11” page of notes
 Bring a calculator if you want (not required)
 Format:
- short answer questions
- Some quantitative/estimation questions
 I will curve the exam
- No one can write a (new) exam and guarantee that an 81% is a B and a
79% a C.
 The exam can be curved both up or down
The midterm exam
 I do NOT expect you to memorize formulas
- Formulas all will follow from dimensions of quantities
 I do NOT expect you to memorize statistics
- but you might want to note down key numbers
 I DO expect you to know “big picture” facts
- The US has a large reserve of coal, but very little oil
 I DO expect you to know important concepts
- Exponential growth, tragedy of the commons, peak oil…
 Studying
- Lecture notes
- Homework
- Discussion questions/projects
- On-line media
Exam
- Today’s lecture will review some concepts
- Note: There are no absences permitted for the exam.
- Only exceptions:
- Health - requires doctor’s note
- University approved absence (requires documentation)
How my first car caused the war in Iraq
 A bad car
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Physics 105 – Fall 2011
Ralph Nader
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Physics 105 – Fall 2011
Florida 2000
The Ballot
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Physics 105 – Fall 2011
Summer 1973 – Datsun (Nissan) 1200
Miles
Gallons
MPG
Cost
Price/gall
on
207
6.9
30
$2.80
$0.40
211
7.2
29.5
$3.00
$0.41
224
7.1
31.5
$2.90
$0.41
217
6.9
31
$2.89
$0.42
Physics 105 – Fall 2011
PHYSICS 105 Mid-term topics
Energy - concepts of energy, work, power; potential/kinetic energy; units (W, J, Wh)
Population - exponential growth; international trends
Tragedy of the Commons - examples of commons; how to prevent Tragedy
Ozone hole- source of problem (CFCs), potential impact; solution (ban); timescale
Electricity - Ohm’s Law; AC vs. DC
Thermodynamics - temperature; 1st law; 2nd law; entropy; heat engine; Carnot efficiency
Electrical Supply - electric grid; peak power; storage
Fossil Fuels - source of fossil fuels; world trends; peak oil
Pollution – Linear no theshold vs non-linear effects, sources of pollution, fracking
Transportation – Energy usage in transportation, hybrids, plug-in electrics, fuel economy
My TV uses 100 W of power when on. I watch TV
4 hours per day. My daily energy usage is:
1.
2.
3.
4.
5.
6.
100 W
100 Wh
400 W
400 Wh
0.4 kWh
400 J
My computer uses 360 W of power when on. The
current my computer draws (@120V) is about:
1.
2.
3.
4.
5.
6.
7.
1 amp
3 joules
3 amps
36 amps
360 W
0.36 kW
360 J
Electricity costs $0.10 per kWh. How much does
it cost to run a 100 W computer 10 hours per day
for 10 days?
1.
2.
3.
4.
5.
$0.10
$1.00
$10.00
$100.00
$1000.00
A perfect heat engine runs between two
temperature reservoirs with temperatures T1 =
227 deg. C, and T2 = 127 deg C. What is its
efficiency?
1.
2.
3.
4.
5.
6.
1%
10%
20%
40%
60%
100%
You may need  = (T1-T2)/T1
T(K) = 273 + T(deg C)
You make $100 a week. You are given a raise of
10% per year. How long will it take for your
salary to double?
1. 5 years
2. 7 years
3. 10 years
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Physics 105 – Fall 2011
You make $100 a week. You are given a raise of
10% per year. How much will you be making in 3
years?
1.
2.
3.
4.
5.
$130
$133
$135
$137
$140
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Physics 105 – Fall 2011
If gas is $4/gal how much does the average
American family spend on gas a year
1.
2.
3.
4.
5.
6.
7.
8.
$1,000
$2,000
$3,000
$4,000
$5,000
$6,000
$8,000
$10,000
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Physics 105 – Fall 2011
 You are the CEO of a large on-line book selling company. Think of
three energy related changes you could make that would both save
energy and make money:
 What are the major changes that peak oil imply?
 Why are population dynamics relevant to energy supply and usage.
 Why did Tesla win and we use AC electrical power supply?
 Name three examples of heat engines.
 Give three examples of the tragedy of the commons and suggest
solutions
 What was causing disappearing Ozone – why is this bad
 How can you reduce the heat loss from your house – explain in
terms of the heat transfer
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Physics 105 – Fall 2011
 What does Peak oil mean?
 Is it possible to have reached peak oil and still have lots of oil in the
ground?
 What is Fracking and why do people do it?
 What is wrong with fracking?
 What is a linear no-threshold model? What are the alternatives?
 Why is the advantage of burning low-sulfur coal?
 Why does the EPA restrict sulfur emissions?
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Physics 105 – Fall 2011
 What are the advantages of hybrid like the Prius over a regular car?
 What are the advantages of a plug-in hybrid like the Chevy Volt
over a regular hybrid like the Prius?
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Physics 105 – Fall 2011
What is the energy source of a Prius?
1. Gasoline
2. Electricity
3. Either
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Physics 105 – Fall 2011
What is the energy source of a Volt?
1. Gasoline
2. Electricity
3. Either
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Physics 105 – Fall 2011
A 100kg student runs up a 5m hill in 10s
What is the power the student is putting out?
1. 50W
2. 100W
3. 250W
4. 500W
5. 50J
6. 100J
7. 250J
8. 500J
Assume g=10m/s2
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Physics 105 – Fall 2011
For the student in the previous problem
Estimate how much power he was using?
1. 100W
2. .5kW
3. 1kW
4. 2.5kW
5. 5kW
6. 500W
Where does the extra energy go?
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Physics 105 – Fall 2011
The following is a selection of slides from previous lectures that
emphasize the main points. If something appears here it does not
necessarily mean that it will be on the exam. If it does not appear
here that does not mean it will not be on the exam.
Physics 105 – Fall 2011
Energy and Power
Energy: the capacity to do work
Work = force X distance
Power: energy per time
Physics 105 – Fall 2011
Energy/ Power Units – know the difference
 Joule = 1 kg m2/s2 - Metric unit of energy
 Calorie (food) = 1 kcal = 1,000 calories = 4186 J
 1 kcal (Calorie) is the equivalent energy to a 100w light bulb on for about 7
minutes
 BTU (British Thermal Unit) = energy to raise temperature of 1 lb of water by one
degree F = 1,055 J = 0.25 Kcal
 Watt is J/s
 kWh = 1000 Joule/s for one hour = 3,600,000 J = 3.6 MJ
 Power = I (current) x V (voltage) -> 1 amp x 1 Volt = 1W
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Physics 105 – Fall 2011
Work
 In physics, the definition of work is the application of a force through a distance





W = F·d
W is the work done
F is the force applied
d is the distance through which the force acts
Only the force that acts in the direction of motion counts towards work
• Kinetic energy : Ekin= 1/2 m v2
•
• Work-Kinetic Energy Theorem:Ekin = Wnet
Physics 105 – Fall 2011
A gallon of gasoline contains 130MJ of energy
 How much would it cost to by the equivalent amount energy at
$0.15 at kWh?
- 1kWh= 1000Jx 3600s = 3.6x 106J =3.6MJ
- (Or From the back of the exam – 1kWh =3.6 x 106J)
- 130MJ/(3.6MJ/kWh = 36.1 kWh
- 36.1kWh *$0.15/kWh = $5.41
 So why do we want to have a plug-in car?
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Physics 105 – Fall 2011
Estimates of Human Population
Green revolution
Industrial revolution
Fire, tool-making
Physics 105 – Fall 2011
World Population
Physics 105 – Fall 2011
Tragedy of the Commons
 Garrett Hardin 1968
- Article is on ELMS
 A commons is an open space
available to all
 Hypothetical case of 10 dairy
farmers using the land
- In hard times everyone has a
few cows and there is plenty of grass for all
- As things improve we assume the that eventually we get 20 cows
each (total 200 cows) and we have reached the carrying capacity
of the land
Physics 105 – Fall 2011
Tragedy of the Commons
 What should a rational farmer do?
- If he adds a cow he gets the benefit of another cow
- However all the cows including his 21 now only get 200/201
(99.5%) of the nutrition it needs produce a full amount of milk
- Mathematically lets say his benefit is +1 from the extra cow but
each cow loses about 0.5% so he loses ~10% of one cow so his
net profit from adding the cow is 9/10 of a cow
- So he should do it
- And so should everyone else
 What happens next?
Physics 105 – Fall 2011
How do we deal with T.o.t.C?
Privatization
If I own the land, it is in my interest to adjust the number of
cows to prevent catastrophe
Regulation
An organization (usually governmental) set rules to make
sure catastrophe does not happen
Physics 105 – Fall 2011
Ozone, Oxygen and Life
Physics 105 – Fall 2011
Ozone Absorbtion of UV
Physics 105 – Fall 2011
Ozone Depleting Substances
 Chlorofluorocarbons (CFCs)
- contain: Cl, F, C
- long-lived, non-toxic, non-corrosive, and non-flammable
- Great as propellants
- in 1960s used in refrigerators, air conditioners, spray cans,
solvents, foams
 The Problem was they were found to migrate to the upper
atmosphere where they would break down and catalyze the
destruction of Ozone.
Fridges used to use ammonia
Physics 105 – Fall 2011
Ozone Hole
 Largest
Antarctic ozone
hole ever
recorded
(Sept. 2006)
Physics 105 – Fall 2011
Ozone Chronology
1978
1979
1981
1982-85
1985
1987
US bans nonessential aerosols
(Canada, Norway, and Sweden)
Germany hosts second UNEP meeting
UNEP council recommends convention
Reagan/Gorsuch/Hodel; DuPont discontinues
research on CFCs alternatives
working group meetings
Vienna Convention
British scientists publish Antarctic data
Montreal Protocol: 50% reduction
CFCs below 1986 by 2000)
Physics 105 – Fall 2011
Conductors and Insulators
 In some materials (metals), some electrons get freed from their
individual atoms and can move through the material
- Conductors e.g. Copper, Aluminum, Gold, Silver, Mercury,…
 In most materials, the electrons are bound to their nuclei and
cannot freely flow
- Insulators e.g. rubber, plastics, ceramics, glass, gases
Physics 105 – Fall 2011
AC/DC
 AC - Alternating Current
V or I
 DC - Direct Current
V or I
Physics 105 – Fall 2011
The Zeroth Law of Thermodynamics
 Temperature - if two objects are in thermal equilibrium with a third
object (like a thermometer) then they are in thermal equilibrium with
each other
- Another way of saying it is that temperature is a measurable
quantity and it tells us about the energy content of an object
- this law asserts that we can define a temperature function, or
more informally, that we can 'construct a thermometer'
Physics 105 – Fall 2011
Thermal Equilibrium
A
Q
B
 if Q=0 then we are in “thermal equilibrium”
 TA = TB

Physics 105 – Fall 2011
Microscopic definition of T:
 ½ mv2 = 3/2 kB T
 v is average speed, kB is Boltzmann constant
- hot means faster motion
 What happens to the motion of molecules/atoms and absolute
zero?
 Kelvin scale – 0 C = 273 K
- Thermal energy proportional to K, not C or F!
http://jersey.uoregon.edu/vlab/Thermodynamics/therm1a.html
Physics 105 – Fall 2011
The First Law of Thermodynamics – Energy
Conservation
 Many statements:
- Energy is conserved
- Heat is a form of energy
- The energy of an isolated system (e.g. the universe) is constant
- Energy is conserved during any change in state.
 Specifically:
- Heat absorbed by a system + work done on the system = change in
internal energy of the system
 Mathematically:
 Q+W=U
 Q is heat, W is work and U is internal energy
Physics 105 – Fall 2011
The 2nd Law of Thermodynamics
 Many formulations:
- It is impossible to convert heat completely into work.
- No perfect engine
- Can’t just pull heat out of the environment
- Heat cannot spontaneously flow from a material at lower
temperature to a material at higher temperature.
- No perfect refrigerator
- In an isolated system, a process can occur only if it increases the
total entropy of the system.
Physics 105 – Fall 2011
Carnot Engine
 The Carnot Engine is an idealized engine that
works in a reversible way
- What is a reversible engine?
- A refrigerator
- By adding work we can take heat from the
cold reservoir and deposits it to the hot
reservoir
- Again - 1st law works
- W+Q1 = Q2
- Notice more heat is delivered than work
done!
 Even a reversible engine is inefficient
Physics 105 – Fall 2011
Carnot Efficiency
 The efficiency of a Carnot Engine
T1 -T2)/T1
 When does the efficiency approach 1?
- When T2=> 0
- Example
- T1= 500oC = 773K
- T2= 0oC = 273K
T1 -T2)/T1= 500/773= 65%
- This says W=65% Q2= 35%
- So if we take 100J from T1 we get 65J of work
- Redo if T1 is 100oC = 373k
T1 -T2)/T1= 100/373= 26%
- so our 100J of energy only gives us 26J of work
Physics 105 – Fall 2011
Efficiency
 First Law efficiency
- Work out/ energy in
 Second Law efficiency
- Work out/ Maximum possible work out using the same energy
input
Example - heating a house with electricity
use resistive heating - first law efficiency = 100% - sounds good!
use heat pump - can do much better (because we are using electricity
to move energy from outside to inside) - first law efficiency > 200% !!
Second law efficiency always less than 100%
Tells you what the absolute best you can do is…
Physics 105 – Fall 2011
U.S. Energy End Uses
U.S. Energy End Uses
Commercial
18%
Industrial
33%
Transportation
27%
Residential
22%
Physics 105 – Fall 2011
Peak Power
 Customers use 1000W hairdryers between 7 and 8 AM for 5
minutes. How much power should I plan for?
60 000
50 000
40 000
30 000
20 000
10 000
10
20
30
40
50
500 customers…
Physics 105 – Fall 2011
The US Power Grid
Physics 105 – Fall 2011
Losses in Power Transmission
 V=IR
 Power transmitted is P=VI
 Power dissipated by P= I2R
 Ploss = I2R =P2/V2 R
 So for fixed power transmitted the higher the voltage the lower the
current and the less the loss
 Modern Transmission runs at
380KV to 735KV
Physics 105 – Fall 2011
Insulation
Heat transfer:
-Radiation
-Convection
-Conduction
Physics 105 – Fall 2011
Where Fossil Fuels Come From
 There are three major forms of fossil fuels: coal, oil and natural gas.
All three were formed hundreds of millions of years ago before the
time of the dinosaurs - hence the name fossil fuels. Many were
formed in the Carboniferous Period. It was part of the Paleozoic
Era. "Carboniferous" gets its name from carbon, the basic element
in coal and other fossil fuels.
 The Carboniferous Period occurred
from about 360 to 286 million years
ago. At the time, the land was
covered with swamps filled with huge trees, ferns and other large
leafy plants. The water and
seas were filled with algae.
Physics 105 – Fall 2011
Oil
 Most scientists agree that oil comes
from creatures the size of a pinhead.
These one-celled creatures, known as
diatoms, aren't really plants, but share
one very important characteristic with
them - they take light from the sun and
convert it into energy
 Diatoms float in the top few meters of
the oceans (and lakes - which is part
of the reason why not ALL oil comes
from ocean deposits!) and also
happen to be a major source of food
for many forms of ocean swimmers.
Physics 105 – Fall 2011
Coal
 Coal is a hard, black colored rock-like substance.
 It is made up of carbon, hydrogen, oxygen, nitrogen and varying
amounts of sulfur.
 There are three main types of coal –
 Anthracite (90% carbon)
- the hardest and has more carbon, which
gives it a higher energy content
 Lignite (30% carbon)
- the softest and is low in carbon but high in hydrogen and oxygen
content.
 Bituminous is in between. (50-75% carbon)
Physics 105 – Fall 2011
World coal
reserves in
1999
Physics 105 – Fall 2011
Coal
Physics 105 – Fall 2011
How much would raising gas prices
$2/gallon cost the average US family?
1.
2.
3.
4.
5.
$500/yr
$1000/yr
$1500/yr
$2000/yr
$2500/yr
Physics 105 – Fall 2011
Hubbert’s peak
Physics 105 – Fall 2011
Hirsch Report of DoE 2005
 World oil peaking is going to happen, and will likely be abrupt.
 Oil peaking will adversely affect global economies, particularly
those most dependent on oil.
 Oil peaking presents a unique challenge (“it will be abrupt and
revolutionary”).
 The problem is liquid fuels (growth in demand mainly from
transportation sector).
Physics 105 – Fall 2011
Growth in developing countries
Physics 105 – Fall 2011
http://www.gaslandthemovie.com/trailer/
http://www.gaslandthemovie.com/whats-fracking
http://www.pbs.org/now/shows/613/index.html
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Physics 105 – Fall 2011
Fossil Fuel Pollutants








Carbon Dioxide CO2
Carbon Monoxide CO
Hydrocarbons
Nitrous Oxides Nox
Particulates
Sulfur Dioxide SO2
Volatile Organic Compounds (VOC)
Ozone O3
 American Lung Association estimates 27,000 to 58,000 deaths per
year from air pollution
Physics 105 – Fall 2011
VW Golf GTI
~v/A for small v
1/Cv2 for high v
Physics 105 – Fall 2011