Download Joules 1.36 pound

Clicker Question
If you drop a 12 pound ball a distance of 4 feet, what is the
kinetic energy just before it hits the ground?
A)
B)
C)
D)
E)
12 Joules
48 Joules
12 foot-pounds
48 foot-pounds
12 BTU
Work = Force x Distance
Another (sometimes useful) unit of energy is the foot-pound.
1 foot - pound  1.36 Joules
Important Notice
Last Name, First Name
Assignment #
There must be clearly typed in the upper left corner of all
turned in assignments – homework, extra credit, etc.
Otherwise penalty of -2.
Also, for future assignments, all extra credit must be typed
and homework if hand written must be very neat…
400 horsepower and 450 foot-pounds of torque
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.
I will scan Chapter 3 and post on D2L (last one)…
Homework Assignment
Homework Assignment #2
is due Wednesday, January 27, 2015 at 4:30 pm.
It must be handed in to the Wooden Box on the Duane G2B level.
Problem #4 had 18^8 which should be 10^8.
-- My office hours are Monday 1-2 pm,
Tuesday 11 am –12 pm
Also available by appointment – just email me.
-- The class Teaching Assistants will also be available in the
Physics Help Room (downstairs on the Duane 2B level).
Prasanth Prahladna : Tuesdays 3-4 pm, Paul Quelet :
Wednesdays 10-11 am, Ivan Kurz: Wednesdays 11 am – 12 pm
Type of Energy
Another Example - Electrical Potential Energy
PE  U  (electric charge)  (Voltage)  qV

e
force
+
Chemical Potential Energy
Molecules are formed by binding
atoms through sharing of electrons.
These molecules often have stored
electrical potential energy  which we
refer to as chemical potential energy.
We often free this stored chemical
energy through reactions.
Current in external circuit
The amount of stored energy can be
surprisingly large!
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Clicker Question
Most fossil fuels have stored chemical potential energy !
When burning coal, consider the following reaction.
C + O2
This “basketball cannon” demonstration is an example of
converting one form of energy into another. Which are the
correct energy types?
A)
B)
C)
D)
Gravitational Potential Energy  Kinetic Energy
Kinetic Energy  Spring Potential Energy
Chemical Potential Energy  Kinetic Energy
Nuclear Energy  Chemical Potential Energy
C + O2
CO2 + Energy
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).
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.
Thus, note that for every atom of carbon,
we produce one molecule of CO2.
This will turn out to be one of the major factors in the
increase in carbon dioxide in the atmosphere
(a greenhouse gas).
How many atoms are there in 12 grams of carbon?
Avagadro‟s Number = 6 x 1023 atoms per mole
per 12 grams of carbon
A 1 pound lump of coal has about 1025 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
Clicker Question
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.
Other forms of 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
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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.
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.
In fact thermal energy is really just a microscopic form of
kinetic energy.
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.
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)?
Sun is at a high temperature
Electromagnetic radiation emitted peaks in the visible range
(light) which is why we „see‟ the sun
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.
They emit electromagnetic radiation…
The type of radiation depends on the frequency of vibration
and thus the temperature
(characteristic for vibrations in the material)
Potential Energy = m g h
Kinetic Energy = ½ mv2
Heat Energy
We cannot see it
with our eyes (not
hot enough to emit
much visible light),
but we can with an
IR camera
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