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E&E SW 2021

Energy conservation and tracking

Part of the 2021 Summer Workshop:

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Integrating Energy, Equity, and Place �in High School Physics

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Instructor: Rachel E. Scherr, �Assistant Professor of Physics, �University of Washington Bothell

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About me

• I teach introductory university physics
• I collaborate with HS physics and K-8 physical science teachers to improve science teaching and learning (>25 yrs)
• I collaborate with HS teachers to improve energy teaching and learning (>10 yrs)
• I work with the school of education to support future physics teachers (new program)
• I teach physics pedagogy and inclusive teaching to undergrads, grad students, and faculty (>25 yrs)

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Purpose of this session

E&E SW 2021

• Define the physics concept of energy
• Distinguish it from related concepts
• Represent energy with an energy tracking diagram

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This will provide us with:

• A shared vocabulary for energy
• A means to represent energy that is aligned with �the Next Generation Science Standards

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Role of breakout room facilitators

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Facilitators will take the following roles:

• Video recorder
• Timekeeper
• Manager / reminder: e.g., “It says to label the boxes”

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Facilitators may or may not have expertise in my model of energy, so they won’t be “instructors” in that sense.

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Defining energy

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What is energy? – Your model

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Bullet points in session doc

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What is energy? – My model

There are many possible models of energy – including among teachers, and scientists! – so it’s important for me to state mine.

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Energy is a measure of the capacity of interacting objects �to make (physical) change happen. It measures

• the extent of the change that has already occurred, and/or
• the change that can yet occur.

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The capacity to make things happen

A chunk of plastic explosive has the capacity to move objects, make a loud sound, create bright light, etc.

• Energy measures how much change is possible: �how much movement, sound, light, etc.

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A stretched spring can move objects.

• Energy measures how much change is possible: �how much movement the spring can produce.

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Energy is stuff

Energy is like a substance.

• Located in objects
• It can transfer among objects and accumulate in objects
• It can change form
• If the amount in some place changes, it had to come from somewhere or go to somewhere

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Energy is stuff

Energy is like a substance.

• Located in objects
• It can transfer among objects and accumulate in objects
• It can change form
• If the amount in some place changes, it had to come from somewhere or go to somewhere

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“Conservation”

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Related, but different, concepts

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(When defining a concept, it can be helpful to distinguish it from related concepts.)

1. Force
2. Work
3. Qi

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Related concepts: Energy and Force

Energy is a measure of the capacity of interacting objects to make (physical) change happen.

One object can have energy.

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Force is a push or pull – something that, if unopposed, changes the motion of an object.

Force is an interaction between two objects.

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Like a substance.

• Located in objects
• It can transfer among objects and accumulate in objects
• It can change form
• If the amount in some place changes, it had to come from somewhere or go to somewhere

Energy is stuff

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Force is a happening

Like a party.

• Occurs at a particular place/time
• Can be intense or gentle
• Can change the state of objects; both duration and intensity can affect the amount of change
• When it’s over, you can’t take it home with you

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Energy vs. force

A chunk of plastic explosive has the capacity to move objects, make a loud sound, create bright light, etc.

• Energy measures how much change is possible: �how much movement, sound, light, etc.
• Forces make the change happen: Electromagnetic forces between atoms, which make chemistry occur.

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A stretched spring can move objects.

• Energy measures how much change is possible: �how much movement the spring can produce.
• Forces make the change happen: �Forces that the spring exerts on things around it.

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Related concepts: Energy & Work

Energy is a measure of the capacity of interacting objects to make (physical) change happen.

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Work is one mechanism of energy transfer: the kind that occurs when a force pushes an object through a displacement.

In my model, energy is not “the ability to do work”

Energy says how much we can

• Change motion
• Light lamps
• Melt snow
• Charge capacitors
• ...

Work is one of the ways for energy to get from one object to another.

Other ways include warming, radiating, eating...

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Related concepts: Energy & Qi

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• Central to a venerable and effective form of medicine (Traditional Chinese Medicine)
• Often translated as “energy” or something related: “vital energy flow,” “life force,” …
• Has many properties different from the physics model of energy:
• unimpeded flow supports health �and longevity
• not conserved (can be increased)

My model of energy �is culturally specific.

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Forms of energy

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Forms of energy

We cannot observe energy directly, but there are various ways that energy shows itself in the observable world.

Energy comes in many “forms,” which have observable indicators:

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Forms of energy

We cannot observe energy directly, but there are various ways that energy shows itself in the observable world.

Energy comes in many ”forms,” which have observable indicators:

Some forms of energy are grouped together as kinetic energy

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Forms of energy

We cannot observe energy directly, but there are various ways that energy shows itself in the observable world.

Energy comes in many ”forms,” which have observable indicators:

Some forms of energy are grouped together as kinetic energy

Some are grouped together as “potential” energy, which means “energy due to how the parts of a system are arranged”

You won’t hear me use �“potential” to describe energy.

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Forms of energy

We cannot observe energy directly, but there are various ways that energy shows itself in the observable world.

Energy comes in many ”forms,” which have observable indicators:

Some forms of energy are grouped together as kinetic energy

Some are grouped together as ”potential” energy, which means “energy due to how the parts of a system are arranged”

Some are not easily classified

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Forms of energy

A child pushes a loaded wagon �up a hill, starting slowly �and gradually �getting faster and faster.

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Is the wagon gaining:

• Kinetic energy
• Gravitational energy
• Both
• Neither

SLOW…

FAST!

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Zoom poll

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Forms of energy

SLOW…

FAST!

A child pushes a loaded wagon �up a hill, starting slowly �and gradually �getting faster and faster.

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Is the wagon gaining:

• Kinetic energy
• Gravitational energy
• Both
• Neither

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Observing forms

We know there is more �kinetic energy (K) �because we observe the wagon moving faster.

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We know there is more gravitational energy (G) because we observe the wagon getting higher.

SLOW…

FAST!

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Representing energy

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Picturing energy

SLOW…

FAST!

G

K

K

K

K

G

G

G

• Represent energy as �equal chunks of stuff

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• Different forms are �different letters

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Changes in energy

How did more energy get into the wagon?

SLOW…

FAST!

G

K

K

K

K

G

G

G

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Simultaneous Zoom chat

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Changes in energy

How did more energy get into the wagon?

SLOW…

FAST!

G

K

K

K

K

G

G

G

We will always be asking:

• Where did the energy come from?
• Where did the energy go?

The only way the energy of a system �can change is if some energy �enters or leaves the system.

In this case, it came from the child

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Representing the “energy story”

G

K

K

K

CHILD

WAGON

K

K

K

K

• Both the child and the wagon had some energy to begin with: kinetic and gravitational.

G

K

K

K

G

G

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• The child speeds up the wagon by pushing it: the child transfers kinetic energy to the wagon.

• As the wagon moves along the ramp, it gets higher: some of its kinetic energy is transformed into gravitational energy.

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Representing the “energy story”

G

K

K

K

CHILD

WAGON

K

K

K

K

“Energy Tracking Diagram”

• Both the child and the wagon had some energy to begin with: kinetic and gravitational.
• The child speeds up the wagon by pushing it: the child transfers kinetic energy to the wagon.
• As the wagon moves along the ramp, it gets higher: some of its kinetic energy is transformed into gravitational energy.

G

K

K

K

G

G

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Energy Tracking Diagram

G

K

K

K

CHILD

WAGON

K

K

K

K

“Energy Tracking Diagram”

• Objects are areas (boxes)
• Units of energy are letters; letter specifies form of energy
• Energy transfers and transformations are represented with arrows

G

K

K

K

G

G

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Arrows in Energy Tracking Diagram

Transfers: Processes that cause energy to cross the boundary of an object or system

• Shoving
• Warming (thermally conducting)
• Electrically conducting
• Radiating (shining)
• Eating
• …

Transformations: Processes that change energy from one form to another

• Melting, freezing
• Squeezing, stretching
• Metabolizing
• Rubbing/warming
• Glowing (incandescence)
• …

Arrows in an ETD represent energy transfers or transformations. We can identify many types of each:

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Arrows in Energy Tracking Diagram

G

K

K

CHILD

WAGON

K

K

K

G

K

G

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Arrows in Energy Tracking Diagram

G

K

K

CHILD

WAGON

K

K

K

G

K

G

Shoving (mechanical work): Transfers K

Lifting: Transforms K to G

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You try it! Create an ETD

Work together with a team to create the energy tracking diagram for a tissue box that slides to a stop.

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Breakout rooms

Instructions in session doc

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ETD for tissue box

Things I looked for as a teacher:

• Forked paths?
• Tissue box warming too?
• Mechanisms of transfer/transformation

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Comparing energy representations

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NGSS alignment

• At the macroscopic scale, energy manifests itself in multiple ways, such as in motion, sound, light, and thermal energy. [forms]
• The total change of energy in any system is always equal to the total energy transferred into or out of the system. This is called �conservation of energy. 
• Energy cannot be created or destroyed, but it can be transported from one place to another and transferred between systems. 

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NGSS priority: Conserve energy as you track energy transfers and transformations in physical systems

Cross-Cutting Concept: Energy and matter

Practices: Developing and using models

Disciplinary Core Ideas: PS3-A,B,C

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Classic diagrams: Not NGSS-aligned

Bar charts and pie charts show

Energy conservation

Energy forms

They do not show

Energy tracking

Mechanisms of transfer �and transformation

✓

✓

✗

✗

PhET Sims

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Energy simulation

“Energy Forms and Changes” (phet.colorado.edu)

• Energy flows from the biker to the bike chain, and then into the large wheel.
• Some energy occasionally floats off into the surroundings.
• Notice that she gets tired!

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• Similar to ETDs: emphasis on transfer/transformation of energy units
• Energy forms represented by color (not letter)

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Energy Tracking Diagram of simulation

E

BIKER

BIKE CHAIN� + BELT

E

WHEEL

E

E

E

E

E

E

E

AIR

• Energy flows from biker to chain/belt, then into large wheel.
• Some energy transfers to the air.
• Biker’s energy is depleted.

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Energy Tracking Diagram of simulation

B

BIKER

BIKE CHAIN� + BELT

K

WHEEL

B

K

B

K

K

K

T

AIR

I like emphasizing forms (different letters) because forms connect to observable quantities. PhET emphasizes the unity of energy (letter E for all forms).

• Energy flows from biker to chain/belt, then into large wheel.
• Some energy transfers to the air.
• Biker’s energy is depleted.

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Arrows in Energy Tracking Diagram

B

BIKER

BIKE CHAIN� + BELT

K

WHEEL

B

K

B

K

K

K

T

AIR

Mechanical work: Transfers K

Rubbing: Transforms K to T

Labeling raises a question:

I don’t think there is a process by which “B energy” in the person transfers/transforms directly to K energy in the bike chain.

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A complete “energy story,” arrow by arrow

K

BIKER

BIKE CHAIN� + BELT

K

WHEEL

K

K

K

K

K

K

T

AIR

B

B

B

• B energy in the biker transforms to kinetic energy in the biker, by metabolism
• Kinetic energy in the biker transfers to kinetic energy in the bike chain/belt, by mechanical work
• Kinetic energy in the bike chain/belt transfers to kinetic energy in the wheel, by mechanical work
• Kinetic energy in the bike chain/belt transfers/transforms to thermal energy in the air, by dissipation (rubbing/warming)

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A complete “energy story,” track by track

K

BIKER

BIKE CHAIN� + BELT

K

WHEEL

K

K

K

K

K

K

T

AIR

B

B

B

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The biker exercises and pushes the belt, which pushes the wheel.

The biker exercises and pushes the belt, which warms the air by dissipation.

For future analysis: �Which process actually accounts for more of the energy?

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Your next Energy Tracking Diagram

Create an energy tracking diagram for a steam-powered light bulb.

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Breakout rooms

Instructions in session doc

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Energy forms and changes

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Now you can:

• Identify the NGSS model of energy
• Distinguish this from related models
• Create and interpret an Energy Tracking Diagram