Download Lecture 6 - University of Colorado Boulder

Clicker Question
The best coal (Anthracite) which is 88% carbon, has an
energy content of 13,300 BTU / lb.
So how many degrees can you raise the temperature of
260 pounds of water with the energy from one pound of
coal?
A)
B)
C)
D)
E)
5 degrees Fahrenheit
50 degrees Fahrenheit
250 degrees Fahrenheit
3000 degrees Fahrenheit
40 degrees Celsius
13,300 BTU raises the temperature of 1 lbs of water by 13,300 0F
OR
13,300 BTU raises the temperature of 260 lbs of water by
13,300 / 260 = 50 0F
Extra Credit #1 – Write a one page brief on the recent Iowa oil
spill. What are the scientific details and environmental
impacts? How might we gauge how “big” 138,600 gallons is?
Relative to other spills?
Must include all references (at least 2) and
why you believe them to be reliable.
Due in class on Friday, February 3, 2017. Must be typed.
Reading Assignment
All of Chapter 3 was for last Friday. Start reading all of Chapter 4
for the end of this week. Read 4.1-4.4 for Wednesday.
Homework Assignment
Homework Assignment #2
is due Wednesday, February 01, 2017 at 4:30 pm.
It must be handed in to the Wooden Box on the Duane G2B level.
Extra Credit #1 due on Friday, February 3, 2017 in class.
-- My office hours are Monday 11 am - noon,
Also available by appointment – just email me.
-- This week the class Teaching Assistants will also be available in
the Physics Help Room (downstairs on the Duane 2B level).
Phil : Mondays 2 - 3 pm; Joanna : Wednesdays 9 -10 am
Dushyant: Wednesdays 11 am -12 pm; Andrew: Wednesdays 2–3 pm
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sustainable energy
9 course certificate program for
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How do you earn the certificate?
• Three required courses:
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1
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What are certificate program
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Most fossil fuels have stored chemical potential energy !
When burning coal, consider the following reaction.
http://www.colorado.edu/rasei/education/under
graduate-energy-certificate
Applications due between
February 1 and March 1
Sarah Rogers, Energy Education Program Manager ENVS
[email protected]
Adam Reed, Energy Education Director RASEI
[email protected]
C + O2
CO2 + Energy
Energy comes from re-arrangement of orbital electrons.
Note that the nuclei of atoms are not involved
(i.e. not a nuclear reaction).
Energy appears as the Kinetic Energy of the product(s).
Products are “hot” (energy transferred by collisions).
Clicker Question
Each reaction with a carbon atom (in the coal for example), has
an energy of 10-18 Joules.
This seems like a tiny number! But it is only one carbon atom.
How many atoms are there in 12 grams of carbon?
Avagadro’s Number = 6 x 1023 atoms per mole
per 12 grams of carbon
1025
A 1 pound lump of coal has about
atoms of carbon. Thus
the total energy from this chemical reaction is:
Total Energy  Energy per Carbon Atom (# Carbon Atoms)


Total Energy  10-18 Joules/Atom  (1025 Atoms)  107 Joules
With this energy (107 Joules), approximately how many feet
can we raise a 3000 lb car? Assume 100% efficient use of
this energy.
Unit Conversions:
A) 4 feet
1 Joule = 0.74 foot-pounds
B) 10 feet
1 Joule = 0.0009 Btu
C) 200 feet
1 Joule = 0.24 calories
D) 2300 feet
Solution:
 0.74 ftlbs 
Energy  (107 J )  

J


Energy  7 106 ft  lbs
Thus, the work that can be
done is lifting a 3000 lbs car
x 2300 feet ~ 7 x 106 ft-lbs.
2
Capacitors store Electrical Potential Energy
Type of Energy
Another Example - Electrical Potential Energy
PE  U  (electric charge)  (Voltage)  qV

e
force
+
Current in external circuit
* Really Chemical Potential Energy is Electrical in nature.
Other forms of Energy?
New From of Energy = Thermal Energy !
Heat was a confusing concept until the mid-1800’s.
Prior to that it was thought of as some type of fluid
that made things hot.
In fact thermal energy is really just a microscopic form of
kinetic energy.
Hammering a nail into a board.
1. Work is done by the person to give
Kinetic Energy to the hammer.
2. The hammer then does work on the nail to give it kinetic
energy (the nail moves with some velocity).
3. When the nail stops moving, where did the energy go?
Thermal Energy
Thus, when we convert energy into thermal energy, the
kinetic energy is not seen as the net motion of a large object
(like a car or a nail), but instead as an increase in the velocity
of individual particles with random motion.
Heat is the flow of energy between a high T and low T system.
What happens when electrically charged objects
accelerate (slow down, speed up, change direction)?
Since the motion is random, the object does not appear to
move, but just has a higher temperature.
Temperature is typically proportional to the average Kinetic
Energy of particles in a material.
Note that thermal energy can be hard to use (get at) or
convert into other forms.
They emit electromagnetic radiation…
The type of radiation depends on the frequency of vibration
and thus the temperature
(characteristic for vibrations in the material)
3
Sun is at a high temperature
Electromagnetic radiation emitted peaks in the visible range
(light) which is why we ‘see’ the sun
Potential Energy = m g h
Objects like us, the table, the walls are at a lower temperature,
but still emit electromagnetic radiation – just in lower energy
photons in the Infrared Radiation (IR).
An infrared camera can
measure this radiation and
thus determine the
temperature of an object.
Kinetic Energy = ½ mv2
Heat Energy
1 Jelly donut
(250 Calories)
We cannot see it
with our eyes (not
hot enough to emit
much visible light),
but we can with an
IR camera
CO2 + H2O + Energy
How many Joules of energy is this?
 1000 calories   4.184 Joules 
250 Calories  


 1 Calorie   1 calorie 
 106 Joules !
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