PHY111: Summer 201253

Lesson 03: Energy Part II

- Energy Vocabulary- Energy Conservation- Work/Energy/Power Calculations

1/18

Brainstorming

2/18

• “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)

Type type type

The next slide shows the main ideas this brainstorming should have covered!

Brainstorming Organized!

3/18

• 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

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!)

4/18

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!

How the Drinking Bird Works!

5/18

HEAT ENGINE!

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.

A Bit of Humor

6/18

[Total] Energy is Boring“Energy Conservation Principle” a.k.a. “Energy Conservation” a.k.a. “Energy is Boring!”

• What is the basic idea, here?• …formal definition…

• How does this relate to our Universe?

• What happens to our “useable” Energy? (Efficiency?)

• How does this Energy Conservation concept help us?• Energy “accounting”!

• Is Energy REALLY “conserved”??

7/18

NOW LET’S WATCH SOME INSTRUCTIONAL (but FUN) PHYSICS VIDEOS on ENERGY CONSERVATION!

Heat as Energy (KE!)

Energy Song!

ROADY!

Potential Energy

Poem:Energy is Boring, by D. LaFazia

8/18

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.

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 learned today in science class, of the most boring thing!Energy total does not change, but rather stays the same!

I now know that an object,Is not as simple as it seems.And Thermal is to Kinetic,As ointments are to creams.

I learned today in science class, of the most boring thing!Energy total does not change, but rather stays the same!

It seems that Electrical can be looked atIn 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 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 so many types and forms, and ways they are the same!Good gracious it's a mercy, that Total Energy's so lame!

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

10/18

“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 incorrectinformation. 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!

Group Examples:

11/18

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 #39#15#16#17#18#19#26#28

Some Useful Energy FormulaeKinetic Energy:

½·m·v2 (½mv2)

Gravitational Potential Energy:

m·g·h (mgh)

Elastic Potential Energy:

½·k·x2 (½kx2)

12/18

For all of these, …

m = mass of objectv = speed of objectg = acceleration due to gravity (9.8 m/s2)h = height object has the potential to fallk = elastic constant of materialx = distance material is stretched or compressed

PowerThis is a simple enough one…and we’ve actually discussed it during our initial Brainstorm, if you remember.

P = W / t

P is PowerW is Work (in machines, this is usually considered Energy used to perform a function).t is time

13/18

W P t

“Triangle Method”(cover-up what you want to solve for!)

P = W / t

W = P * tt = W / P

EFFICIENCYYou 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 mypersonal favorite), write down the time it takes to complete a full swing for each of the 5 heights (repeat thisexperiment 3 times and get an average before movingon to each new height value).

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

http://stopwatch.onlineclock.net/

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)

16/18

• http://dev.physicslab.org/Document.aspx?doctype=5&filename=Compilations_CPworkbook_ConservationEnergy.xml

• http://dev.physicslab.org/Document.aspx?doctype=5&filename=Compilations_CPworkbook_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!

Study/Practice Worksheets!• http://dev.physicslab.org/Document.aspx?doctype=5&filename=Compilations_CPworkbook_ConservationEnergy.xml

– Hints:Section 1) Think “Energy transformation” and “Total Energy is boring!”Section 2) Variation on the Work-Energy theoremSection 3) Look at first situation and determine Total EnergySection 4) Look at bottom of ramp and determine Total EnergySection 5) Look at top of person’s fall and determine Total EnergySection 6) How are KE and speed related?

• http://dev.physicslab.org/Document.aspx?doctype=5&filename=Compilations_CPworkbook_WorkEnergy.xml

– Hints:Section 1) recall Work and Power calculationsSection 2) start from the 3rd question and work your way back to the 1st Section 3) GPE at the top = KE at the bottom (so set equations equal!)Section 4) The two extremes are a straight drop and an infinitely long rampSection 5) Look at the bottom and decide on what the Total Energy isSection 6) Actually is same logic behind Section 3 (the ramps)Section 7) Total Energy is boring!

17/18Note: These really should not take too long. The latest lab material (pendulum lab) helped a lot with these.

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.

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