PHY111: Summer 201253
Lesson 03: Energy Part II
-
Energy Vocabulary
Energy Conservation
Work/Energy/Power Calculations
1/18
Brainstorming
• “What words/phrases do you think of when you hear the word Energy”?
• Here is what the class came up with: (do in groups, first, then SHARE)
Electromagnetic
Sun/Solar
Voltage & Current
Geothermal
Potential Energy
Fuel
Nuclear
Thermodynamics
Conservation of Energy!!!
Elastic PE
Stored
Gravitational PE
Kinetic Energy
Wind
Electricity
Calories/CHEMICAL PE
Thermal
Work
Hydroelectric (think Niagara Falls problem)
The next slide shows the main ideas this brainstorming should have covered!
2/18
Brainstorming Organized!
• Here are the main points – I have created these based on the most important
brainstorming results that typically are brought up at this point.
Definitions:
• Force: A push or a pull…. “a way to transfer Energy”
• Work: Force “times” displacement
• Power: Work done over a period of time
• Efficiency: How well Energy is used to do Work (friction is important!)
• Thermal Energy: Kinetic Energy of the particles of a substance (small scale)
• Wave: (another) way to transfer Energy
Types of Energy:
• “Mechanical” (an “umbrella” category for other specific types of Energy)
• Kinetic Energy (Energy of Motion), Gravitational Potential Energy (Energy of
height / position), and Elastic Potential Energy (Energy stored in an elastic /
springy material that is stretched or compressed)
• Chemical Potential Energy (batteries, explosives, fossil fuels, food; does it burn?)
• Electrical (Potential—“Voltage”…Kinetic—“Current”)
• Radiant Energy (Solar, ex. Photosynthesis, “light,” Infra-red, visible light, Xray, &tc.)
• Nuclear (fission, fusion, NUCLEAR decay processes, other important
names)…basically a change in a nucleus
3/18
If you were
absent, step
outside into the
hallway for a few
mins!
Energy Transformations
(self-grading)
• There are few better ways to learn from your
mistakes than by grading an assignment, yourself.
• Using a different color ink/lead, make corrections
(and notes to yourself) as we go over the solutions to
the webquest.
• IF YOU GOT AN ANSWER COMPLETELY WRONG,
then in that different color ink/lead place an X on the
# for the question. Don’t forget to make notes to
yourself on the paper to include the correct answer!
This will help you in your future study (AND on tests!)
This grading process is integrated into the ten points for the assignment.
This is a formative activity, so you only lose points if you leave it ungraded!
4/18
How the Drinking Bird Works!
For the one group which already looked at this last
week, you have a special job: Define “Heat Engine”
and identify (2) other examples. You will share this
with the class when we are all ready.
HEAT
ENGINE!
5/18
A Bit of Humor
6/18
[Total] Energy is Boring
“Energy Conservation Principle” a.k.a. “Energy Conservation” a.k.a. “Energy is Boring!”
•
NOW LET’S WATCH SOME INSTRUCTIONAL (but FUN) PHYSICS
What
is on
the
basicCONSERVATION!
idea, here?
VIDEOS
ENERGY
at at home)
•(Look
…formal
definition…
Heat as Energy (KE!)
• How
does
Energy
Song!this relate to our Universe?
ROADY!
• What
happens to our “useable” Energy? (Efficiency?)
Potential Energy
• How does this Energy Conservation concept help us?
• Energy “accounting”!
• Is Energy REALLY “conserved”??
7/18
Poem:
Energy is Boring, by D. LaFazia
I learned today in science class, of the most boring thing!
Energy total does not change, but rather stays the same!
I learned today in science class, of the most boring thing!
Energy total does not change, but rather stays the same!
It may transform by changing type,
Or be transferred from place to place,
But never is it made again, or destroyed...
...which can be a hard fact to face.
It seems that Electrical can be looked at
In this way and in that.
Oh thank goodness that Total Energy,
Has a graph that's always flat!
I learned today in science class, of the most boring thing!
Energy total does not change, but rather stays the same!
I learned today in science class, of the most boring thing!
Energy total does not change, but rather stays the same!
Things that move must have Kinetic,
But it does not stop there.
To be a learned scientist,
Of the Potentials be aware.
I hope that I can keep in mind,
The different things I've learned.
Who ever thought of all these terms,
My thanks has certainly earned!
I learned today in science class, of the most boring thing!
Energy total does not change, but rather stays the same!
I learned so many types and forms, and ways they are the
same!
Good gracious it's a mercy, that Total Energy's so lame!
I now know that an object,
Is not as simple as it seems.
And Thermal is to Kinetic,
As ointments are to creams.
8/18
Discuss in small groups
“You push a heavy box across a rug from one side of a room to the other.”
*) What type of Energy did you need to be able to do this in the first place?
*) Explain how both Elastic Potential Energy and Kinetic Energy were
involved in this process.
*) Once the box is sitting still again, what has happened to the Energy
you used to move it? Be specific in your explanation!
*) Let us say you put 1000 “units” of Energy into moving the box, overall.
If there is no other Energy to be accounted for, how many “units” of Energy
are left from that original amount?
9/18
Discussion Soln’s
“You push a heavy box across a rug from one side of a room to the other.”
1) What type of Energy did you need to be able to do this in the first place?
CHEMICAL Potential Energy
2) Explain how both Elastic Potential Energy and Kinetic Energy were
involved in this process.
Various answers, depending on correctness. Typical response:
EPE with muscles, KE with movement of box
3) Once the box is sitting still again, what has happened to the Energy
you used to move it? Be specific in your explanation!
Now is THERMAL Energy (will accept “Heat” as a response). Be
careful not to have said TOO much, because points taken off for incorrect
information.
Bonus) Let us say you put 1000 “units” of Energy into moving the box, overall.
If there is no other Energy to be accounted for, how many “units” of Energy
are left from that original amount?
1000 units are left. ENERGY is BORING!
10/18
Group Examples:
Form groups of 2 or 3 students.
In your small group, complete the following problems and prepare to present
these to the class (I will assign each group their problems).
p. 98:
p. 101
#14(1)
#15(2)
#16(3)
#17(4)
#18(5)
#19(6)
#26(1)
#28(3)
#39(5)
11/18
Some Useful Energy Formulae
Kinetic Energy:
½·m·v2
(½mv2)
Gravitational Potential Energy:
m·g·h
(mgh)
Elastic Potential Energy:
½·k·x2
(½kx2)
For all of these, …
m = mass of object
v = speed of object
g = acceleration due to gravity (9.8 m/s2)
h = height object has the potential to fall
k = elastic constant of material
x = distance material is stretched or compressed
12/18
Power
This is a simple enough one…and we’ve actually discussed it during
our initial Brainstorm, if you remember.
P=W/t
P is Power
W is Work (in machines, this is usually considered Energy used to
perform a function).
t is time
“Triangle Method”
(cover-up what you
want to solve for!)
W
P t
P=W/t
W=P*t
t=W/P
13/18
EFFICIENCY
You generally have an understanding of this one, already. We know
that you never get more out of a process than what we put into it…
all due to frictional forces of some sort!
%eff = (Wout / Ein) * 100
%eff is “Percent efficiency” (the 100 is used to convert to a
percent)
Wout is how much Work we got out of the system
Ein is how much Energy (sometimes considered Win) was put into
the system.
14/18
Lab: Pendulum
• Exploring GPE to KE transformation and Energy Conservation
•
Materials Needed: Hanging mass, meter stick, stopwatch; lab stand w/clamp.
Step One: Choose a mass to hang from the clamp.
Step Two: Choose 5 different heights (measuring from the
lowest point of descent up to the chosen release point) from
5cm to 50cm [a.k.a. 0.05 to 0.50 meters range].
Step Three: Calculate the GPE stored before the release of
the mass for each of the 5 heights.
Step Four: Using a stopwatch (see link, below, for my
personal favorite), write down the time it takes
to complete a full swing for each of the 5 heights (repeat this
experiment 3 times and get an average before moving
on to each new height value).
http://stopwatch.onlineclock.net/
Post-Lab Analysis:
•
How should the KE for each trial compare at the bottom of the swing to the GPE at that initial height?
•
How should the GPE initially compare to the GPE at the top of the swing on the OTHER SIDE?
•
What do your times-of-swing tell you about the SPEEDS at the bottom of the swings in terms of from what
height the mass was originally released? (I know this is poorly worded, but what do you make of it?)
•
When should the KE and GPE be EQUAL at the same moment in time for a pendulum system?
•
Derive an equation that will allow you to find the final speed for an object dropped from a given height if the
mass of the object is unknown (this should be a fun one…feel free to ask for a hint!)
15/18
Grades/Assignments:
Read Sections 8.4-8.6.
Lab 3 should be turned in before you leave.
Practice the following: (hints provided for these on the next
slide)
•
•
•
•
•
http://dev.physicslab.org/Document.aspx?doctype=5&filename=Compilations_CP
workbook_ConservationEnergy.xml
http://dev.physicslab.org/Document.aspx?doctype=5&filename=Compilations_CP
workbook_WorkEnergy.xml
(You may need to copy + paste the above links)
THIS WILL NOT be turned in. These are for PRACTICE. This is a great opportunity
to form a study group to work through these.
See hints on the next slide!
16/18
Study/Practice Worksheets!
•
http://dev.physicslab.org/Document.aspx?doctype=5&filename=Compilations_CPworkbook_ConservationEnergy.xml
– Hints:
Section 1)
Section 2)
Section 3)
Section 4)
Section 5)
Section 6)
•
Think “Energy transformation” and “Total Energy is boring!”
Variation on the Work-Energy theorem
Look at first situation and determine Total Energy
Look at bottom of ramp and determine Total Energy
Look at top of person’s fall and determine Total Energy
How are KE and speed related?
http://dev.physicslab.org/Document.aspx?doctype=5&filename=Compilations_CPworkbook_WorkEnergy.xml
– Hints:
Section 1)
Section 2)
Section 3)
Section 4)
Section 5)
Section 6)
Section 7)
recall Work and Power calculations
start from the 3rd question and work your way back to the 1st
GPE at the top = KE at the bottom (so set equations equal!)
The two extremes are a straight drop and an infinitely long ramp
Look at the bottom and decide on what the Total Energy is
Actually is same logic behind Section 3 (the ramps)
Total Energy is boring!
Note: These really should not take too long. The latest lab
material (pendulum lab) helped a lot with these.
17/18
Looking Ahead:
Lesson 04 will be an online lesson. We will continue to discuss
energy transformations, will go over some useful solutions,
and will explore an application of these concepts using a
hydraulic jack.
You will also be given an overview of Test I material, as next
Wednesday will be your online/take-home test.
18/18