ALISON Guide to Heat and Energy Activities for the … Guide to Heat and Energy Activities for the Classroom Marc Swanson (Seward Elementary, retired) Cheryl Abbott (Wasilla High School)

ALISON Guide to Heat and Energy Activities for the Classroom

Marc Swanson (Seward Elementary, retired) Cheryl Abbott (Wasilla High School)

Summer 2005

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Project ALISON: Using Lake Ice to Understand Heat Conduction

ALISON provides a unique experience for Alaskan students. Participating classrooms have the opportunity to become part of an important baseline study to better understand winter heat exchange in Alaska lake systems. Using scientific procedures and instruments students gain the satisfaction that they are collecting valuable data for a genuine scientific research project. But it is more than that. ALISON allows students of all ages to better understand the concept of heat flow. Students already come into the classroom with an pretty good understanding of heat. They know if they touch something hot they’ll get burned. If they touch their tongue on a metal gate post on a ‘balmy’ winter day in Fairbanks, they’ll become quite attached to their project. They already have an intuitive understanding, and interest, in conductive heat flow. It is our job, as teachers, to tap into the students’ interest, preexisting knowledge, and misconceptions to create a unit of study that builds on practical knowledge and moves toward conceptual and scientific understanding. The purpose of this booklet is not to present a curriculum of heat flow, but rather to share some ideas that help translate the central concepts of ALISON into a classroom laboratory setting. Most of the activities are designed for mid-dle school aged students, but teachers can easily translate these activities to fit a much broader audience. Finally it is important to remember that this booklet is neither an end-all nor is it all inclusive, but hopefully will rather serve as a nu-cleus from which new ideas will be built. We look forward to the addition, improvement, and refinement of these activi-ties in the future. Marc Swanson: Seward Elementary School, retired Cheryl Abbott: Wasilla High School

From the Authors ….

The ALISON project is made possible through the sup-port of NSF grant OPP 0425884 (Office of Polar Pro-grams, Arctic Social Sciences Program), the Interna-tional Arctic Research Center at the University of Alaska Fairbanks under the auspices of NSF Coopera-tive Agreement OPP-0002239, and the University of Alaska Natural Resources Fund. Funding for the ALISON project was also provided Toyota TAPESTRY Grants for Teachers.

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Table of Contents & Standards

Table of Contents

From the Authors ... 2

ALISON Learning Opportunities 3

We Add Heat … Should Get Hot!: Discrepant Event

7

Hot Rods!: Understanding the Heat Capacity of Water

9

Thermal Conductivity: Insulating Properties of Various Materials

13

Activity Two—Thermal Conductivity of Two Metals

15

Temperature Difference: Exploring the Rate of Heat Transfer

16

Spreading the Temperatures: Exploring Latent Heat

19

Quantifying Latent Heat: Where Have All the Calories Gone?!

21

Thermal Conductivity: Measuring Heat as it Passes Through Various Substances

25

Designing the TWITT: Maintaining Experimen-tal Design

27

How Does Your Ice Grow? A Comparative Study of Ice Development

29

Unlocking the Invisible Ice Crystals 32

How Much is it Worth? 34

Joules vs. Calories—Point and Counterpoint 6

A note on standards: Teachers are often asked to provide verification that classroom activities align to content and performance standards. With this in mind, the following standards have been identified. By no means is this a comprehensive list. The standards listed are taken from the National Science Education Standards (NSES). Teachers participating in AL-ISON can no doubt expand this list as they customize their curriculum.

NSES Unifying Concepts and Processes • Systems, Order and Organization • Evidence, Models and Explanation • Constancy, Change and Measurement NSES Science as Inquiry (K-12) • Asking questions about objects and events in the environment • Planning and conducting a simple investigation • Employing simple equipment and tools to gather data and extend the

senses • Using data and data analysis to con-

struct a reasonable explanation • Communicating investigations and ex-

plorations NSES Physical Science • 5-8 Properties and changes of proper-

ties in matter • 9-12 Structure of atoms, and structure

and properties of matter • 5-8 Transfer of energy • 9-12 Conservation of energy and in-

crease in disorder and interactions of energy and matter

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ALISON Learning Opportunities

One of the strengths of ALISON is the wide variety of age levels and subjects that can be taught using lake ice. The opportunities are endless. In this booklet we are focusing on activities related to heat and energy. But we wanted to take a moment to display some of the other directions a teacher may choose to use ALISON in their curriculum.

ALISON Learning

Opportunities

Heat/Energy Computer Models

Math

Snow/Ice

Geography

Climate Change

Science Process Skills Using ice data to

monitor global cli-mate change.

Human influences on climate change.

Native Knowledge

Using Algebraic equations in real life appli-cations.

Comparing quantitative data.

Local terms for various snow/ice conditions.

Local knowl-edge differ-entiating between safe and unsafe ice.

Conductive Heat Flow Thermal Conductivity Latent Heat of Transformation

Analyzing crystal structure of ice/snow

Avalanche aware-ness.

Snow Ice vs Con-gelation Ice

Observing meta-morphisis of snow crystals.

Accurate measurement. Experimental design and protocol. Drawing conclusions based on data.

Climate vs. Weather Comparing Ice Data in vari-ous climatic regions of Alaska.

Importance and limitations of computer models in sci-entific research

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ALISON Learning Opportunities

If you are lucky, you are employed by a school district that trusts your judgment and treats you as a professional. If you are lucky, you don’t have finger pointing administrators breathing down your neck demanding justification for every item in your lesson plans. If you are lucky, you live in a country that lets you decide the most efficient way to educate students rather than implementing weeks of testing. But let’s be realistic …. There is probably one or two of you out there who will be asked, “How does ALISON fit in our curriculum?” After you shake your head and mutter, “you just don’t get it”, you can throw this at them. ALISON does not teach the concepts of heat and energy in a traditional fashion. But let us assure you it DOES teach all the concepts found in a traditional heat and energy unit. If you look through a “Thermal Energy and Heat” chapter of a high school physical science textbook you may see some terms that are not mentioned in the activities found in this booklet. Below is a list of these terms and how they can be explained using lake ice and the ALISON program.

Conduction— the transfer of thermal energy with no transfer of matter Conduction is what ALISON is all about. Heat traveling through sub-stances (from hot to cold) is key concept #6 (pg 6 in manual). How much con-duction is taking place is quantified when we calculate the conductive heat flow. Conduction can also be found in less obvious places. We teach the stu-dents that snow is a good insulator. It is a good insulator because the air found between the snow crystals does not conduct heat very well. Conduction in gases is slower than in liquids and solids because the particles in a gas col-lide less often. Convection— the transfer of thermal energy when particles of a fluid move from one place to another Convection is often described by discussing convection currents. Con-vection currents are important in many natural cycles such as weather systems and ocean currents. Many lakes also have convection currents circulating warmer and cooler water throughout the lake. If students measure the thick-ness of the ice at various places around the lake they will find that the thick-ness varies. One of the variables contributing to this variation is the natural convection currents circulating in the water under the ice. Radiation—the transfer of energy by waves moving through space ALSION provides multiple opportunities to discuss radiation. Some of them include:

• Taking surface (air) temperatures in the shade or shadow. On one bright February afternoon the difference in temperatures between the shade and direct sunlight was 1.5°C.

• Spring meltdown occurs faster for dark colored objects. The arri-val of the wonderful radiant warmth of spring sun will leave you with 21 mini-holes in the ice and 21 MIA stakes.

First Law of Thermodynamics—energy cannot be created or de-stroyed, but it can be converted into different forms (also known as the Law of Conservation of Energy) Many of the ALISON activities recycle this concept with the students. When a hot rod is put in a beaker of water, the water gains 2,000 calories. But at the same time the rod loses 2,000 calories. The two values must be the same. Calories can’t be added to one substance without being taken out of another… the first law of thermodynamics. Second Law of Thermodynamics—when energy is changed from one form to another, some of the useful energy is always degraded to lower quality, less useful energy (disorder is always increasing) The second law of thermodynamics is the science behind Concept #2 (pg 4 in manual) “temperature determines the direction of conductive heat flow”. In a natural system, such as a frozen lake, heat will flow from hot to cold. Hot to cold. Hot to cold. By the end of the unit the students will have heard this 100 times. The reason is this: for heat to flow from cold to hot, work must be added to the system. Work is something we all avoid, nature included. We are much better at disorder. No energy conversion is 100% efficient. And yet the energy cannot be lost or disappear (see law #1). So where does it go? Thermal energy is often considered a “low quality energy” because it has little ability to do useful work. It can’t make your car go, nor can it power the stereo While a ten degree tem-perature change may be “low quality energy”, when considered as a whole, across wide areas of land and in terms of climate, conductive heat flow may very well be a very big deal. Thus the importance of the ALISON data. Third Law of Thermodynamics—absolute zero cannot be reached Daring to defy nature, scientists have come close, 3 billionths of a de-gree above absolute zero, but no cigar. Including this tid-bit of trivia may add to your discussion of temperature scales.

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Joules vs. Calories: Point and Counterpoint

In the next section of heat related activities, the reader will note, perhaps with some embarrassed confusion, that calories have been used to quantify heat energy while joules is the more accepted standard found in upper level texts. You may find yourself asking, “What gives? Why is it that the authors of this booklet choose to buck the prevailing winds of wisdom and choose this alterna-tive archaic standard? And what is it that the discriminating teacher should present to their charges?” Here to discuss the pros and cons of calories vs joules is for-mer, now retired 6th grade educator Marc Swanson and Wasilla High School teacher, Cheryl Abbott.

Abbott, you impertinent nitwit, Are we, as science teachers, postulated to be like a herd of ne-scient lemmings bound by the ones in front to lose all will and foresight to jump over the cliff only because that is what all others are doing? Nay, I say. We, as independent and free-thinking educa-tors, know that good science means making real connections with real world phenomenon. And calories provide this tangible connection to an otherwise abstract and imperceptible concept of heat energy. Even the most scientifically illiterate of students can get a grasp that one calorie is the heat required to raise a gram of water one degree Celsius. This is not rocket science. In contrast, a joule, to a young student, is merely something that is set on a ring and presented to a girl. And is this something we want to teach in our schools? Nay, I say. Armed with the foundational understanding of 1 calorie, even young scholars will be able to figure the heat exchange when 200 ml of water is raised by 4 degrees C and ultimately, will be able to comprehend the enormous energy exchange required to make a cube of ice for their soda pop. This is what science is all about. And furthermore, are we to change science willy-nilly at a mo-ment’s glance because someone wants a measurement system named after them. Oh please. Would we consider changing the shape of the wheel just because someone wanted infamy and riches? Nay, I say. It’s time to stand and be counted as one of those willing to take a stand. And besides….if you really want to use joules, you could sim-ply multiply the calories by 4.18.

The Verdict and General Disclaimer: By the flip of the coin (point, Marc) the authors chose to write these lessons using the units of calories and 1.0 for the specific heat of water. However joules is the accepted energy measurement (point, Cheryl) and is the one presented in high school texts. We leave it up to you to decide whether to teach joules as a) a conversion from calories or b) as a stand alone measure of energy.

Swanson, listen up you big buffoon, Let me introduce you to someone: the honorable Sir James Prescott Joule. A noble British physicist of the 1800’s who is known for his work in attempting to demonstrate the unity of forces in nature. The joule is the metric unit of work/energy. This little unit is as noble as the physicist that it was named after, for a joule, unlike your calories, can be defined in many ways: • One joule is the amount of work done when a force of 1 Newton moves an object one

meter • One joule of energy per second is required to pass an electric current of 1 ampere

through 1 ohm resistance • One joule per second equals one watt, a unit of electric and mechanical power • And no Swanson, a joule is NOT some lame manly attempt to earn forgiveness from

his lady As you can see, joules have a future, so to speak. They can be applied beyond the world of heat energy. This can not be said of your calories. What can you do with a calorie be-sides obsess about how many of them you’ve consumed during a lonely night alone with a cheesecake? Now I can understand that to a simplistic elementary teacher, this might seem like rocket science, but I assure you, this is NOT rocket science. Nevertheless, I prefer to be-lieve my students are capable of being rocket scientists, biotechnologists, electrical engi-

neers or any other advanced scientific career they may choose. I will not limit their futures to burger flipping or tomato picking with the assump-tion that they are not capable of understanding a number more complex than 1.0. So Swanson, when times change, when technology advances, when sci-entific breakthroughs arise, will you stubbornly cling to outdated termi-nology? Or will you step up to the plate, embracing a more accurate, ad-vanced way of life? The simple fact is calories, in regards to heat energy, are old school, washed up units of the past. Current science uses joules and so will I!

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We Add Heat...Should Get Hot!: A Discrepant Event

Objectives • Students will understand that heat is transferred from warmer to colder substances. • Students will realize that temperature gain and heat absorption may not be the same thing. • Students will effectively graph data and provide possible conclusions for unexpected data.

Other Possible Objectives

• Students will learn that the scientific calorie and food Calorie are different measurements. • Students will conceptually understand that it requires more heat (without temperature gain) to change the state of matter.

Description of Activity Students will heat and monitor the temperature of 200 ml of ice water. They will record temperature changes at regular intervals (1/2 or 1 minute) and note time when water reaches a change of state of matter (ice thaws completely and water boils).

Background Information Note: This activity is being presented as a discrepant event that could lead in to the unit of thermal conductivity. However, this experiment could also fit into understanding latent heat or measuring heat flow. It is merely up to the teacher’s interpretation of how best to use it in the classroom. The students come into the classroom with a good understanding of heat and cold. They live in Alaska… snow and cold are familiar and abundant substances. Therefore it’s not a bad idea to start the unit with an activity that challenges the student’s conceptual understand-ing of heat flow.

No matter whether high school or elementary, the students probably grasp the idea that a pan of water will become warmer on the stove because the heat from the stove is being transferred into the colder water. They probably intuitively realize that, assuming the energy source does not change, the pot of water will heat more less at the same rate. This activity is designed to derail, a bit, this train of thought. Hope-fully the overriding lesson in this activity is that in order to under-stand ALISON we need to look at lake ice a bit differently.

Lab Set Up

Lamp

Slush Water Materials (per Team)

• Stand (for holding beaker during heating)

• 1– Glass Beaker (we used 250 ml) • Alcohol Lamp (or other heat source) • Thermometer

• Timer • Crushed Ice or Snow (of course

snow is best) • Water

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We Add Heat...Should Get Hot!: A Discrepant Event

Procedure:

1. Create a mixture of slush. Ice particles must be small for this activity to work consistently.

2. Establish and measure set amount of ice water (200 ml)

3. Take initial temperature then put beaker under heat source.

4. Take and record temperatures in 30 or 60 second increments. Prior to recording temperature, give the solution a quick stir to mix varying temperatures together. This will provide for more consistent data.

5. Students will note, in the beginning, that although heat is being added to system, there is no net gain in temperature. The temperature will remain at 0ºC until the ice has melted.

6. Make note of the time when ice has melted completely and again when water has begun to boil rapidly. (Note: once ice has melted it is less necessary to stir water prior to recording temperature. It is already fairly well mixed due to convection currents.)

7. As water begins to boil, the temperature gain will slow and eventually level off. This may or may not be at exactly 100° C.

8. Make a graph of the data.

Making Sense of the Data If the students have acquired clean data (as represented by the graph at the right), they should be able to see that the temperature remained fairly steady near 0°C until most of the ice had melted. Then, after climbing steeply the temperature again stabilized near 100°C when the water began to boil hard. The major point to stress is that these plateaus exist even though the rate of heat release (from the lamp) and heat absorption (from the water) remained con-stant. If this lesson has been used at the beginning of the unit as a discrepant event, it should serve as a reminder to students that there is more to heat flow than what they probably know intuitively. It would seem that temperature and heat are synonymous, but indeed this activity suggests otherwise as the amount of heat added was constant, but the temperature did not increase at a constant rate. If the activity has been used to supplement the experiments discussing latent heat, one should check the lesson on latent heat to possibly quantify their results.

TE

MP

T I M E

I C E

B O IL IN G

Disclaimer: Yeah, this graph represents perfect data in a perfect world. Although the students’ data may deviate from this a bit, data should parallel the graph.

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Background Information Many students are confused about the difference between heat and tempera-ture. It is a common misconception among students that the greater the tem-perature, the greater the heat. If you would like to further develop this mis-conception, simply cut a hole in the lake ice and ask a student to go for a swim. They would argue, through chattering teeth, that the lake contains no heat at all. But it does. Vast amounts of heat.

The concept of a frigid lake being a reservoir of heat is central to the ALISON project. The main objective of ALISON is to measure the heat being con-ducted away from the lake water that results in an ever thickening ice layer. Therefore, before students can truly understand why they are taking the measurements for the project, they have to look at their frozen, iced over site as being a huge stockpile of thermal energy. Once they have that concept ingrained into their cerebellum then they will be well on their way to being a crysopheric geophysicist .

Objective: • Students will develop an understanding that temperature differences determine direction of heat flow. • Students will understand that water can hold vast amounts of heat. They will be able to relate this to

the overall objective of ALISON.

Description of Activity

Students will heat a small steel rod with alcohol lamp (or equivalent heat source). While heating the rod, students predict what will happen when the rod is placed in beaker of water (the water will become warmer, the rod will cool). The heat is being transferred from the warmer object to the cooler until they have reached a state of equilibrium (the same temperature). The heat from the rod has been transferred into the water… the evidence is the

temperature change. What will be surprising is that although the rod will be quite hot (perhaps up to 350 degrees C) the change of water temperature is only minimal (perhaps only 5-15°C).

Indeed if we could extract those 5-15° of heat in the water and put it back into the steel rod, it would once again be the original 350°C.

Materials: Per Team: • 1- 1000 ml Glass Beaker with water. • Thermometer • Steel Rod— perhaps 1/2 X 3 inches • Alcohol Lamp (or equivalent heat source) • Tongs for holding rod safely

Setup

Step One

I wish I was an ALISON student!

Step Two

20° CONE REALLY HOT ROD!!!!Let’s say 350 °C

Perhaps28° C

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Procedure: 1. Measure beginning temperature of water. 2. Begin by heating rod above burner. This will take several minutes. During this time discuss why rod is heating up (transfer of heat from

flame to rod). Then discuss what will occur when it is put into the water. (Heat transfer to water. Evidence would be that the rod will cool down; water will heat up).

3. Place rod into water. Be careful not to drop rod into glass beaker. Stir water for a few moments and measure temperature. It should not

take but a moment or two for the temperature to stabilize. Depending on the temperature of the rod, water, and mass of rod the tempera-ture should rise only 5– 15 degrees C.

Making Sense of the Data Graphing the heat loss/ gain will allow students to better visualize the transfer of heat. Discuss with students that the loss of temperature in the rod and the gain of temperature in the water illustrates heat being transferred from the warmer object to the cooler. In this example (a net gain of 15 degrees C) is a result of the heat in the rod being transferred (with some loss) to the water. If this net gain of heat could be extracted and put back into the rod, then the rod would return to its origi-nal temperature.

The Application:

All bodies of water represent store houses of heat energy. In particular, the ocean is a huge reservoir of heat energy that affects climate on a local and global level. A quick look at an Alaskan weather map will illustrate this nicely. In the winter, while those poor souls in Nome, Barrow, and Fairbanks are driving on temperature hardened tires, those folks along the coast in Seward and the Southeast are enjoying (?) rain and slush. In the summer, when heat is being absorbed by the ocean, the interior is enjoying hot weather and wagon sized cabbages while the coastal folks are still wearing fleece and rain jackets. It may not seem fair but it is the heat capacity of water at work.


Heat Transfer from Rod to Water

0

50

100

150

200

250

300

350

400

St eel Rod

Wat er

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The Math:

This may be a good time to introduce the equation for calculating the amount of heat gained or lost by a substance. With the data the students have already recorded, the amount of heat transferred from the rod into the water can be calculated. While the letters and symbols may be in-timidating, the equation is nothing more than a simple multiplication problem.


Let’s say there is 300 ml of water in the beaker. The water in the beaker goes from 20°C to 28°C . With

this information we can calculate the amount of heat added to the water by the metal rod.

calories 240018300

=×°×=

QCgQ

shTmQ ×Δ×=Q= Heat Exchange in Calories

m = the mass of the water (300ml = 300 g)

ΔT= Tend– Tstart (28°-20° = 8°C)

sh = the specific heat of water is 1 cal/g °C

Q = amount of heat transferred ( A negative number means heat was lost. A positive number is heat gained.)

m = mass of substance (Remember, for water 1ml=1g) ΔT = change in temperature (ending temperature minus starting temperature) sh = specific heat of the substance (The specific heat of water is 1 cal/g °C.)

Note: This lesson uses the scientific unit calorie even though this unit of heat measure is being replaced by the internationally recognized unit of energy, the joule (J). Conceptually it is more difficult to use the joule in this activity. However, calories can be easily converted to joules with this formula: Joules = Calories X 4.18. For more information, check out the Point/Counterpoint discussion of using Joules vs Calories.

Perhaps 20° C

One Really HOT ROD.

Perhaps 28° C

300 ml

An Example

The Formula

startend TTT −=Δ

shTmQ ×Δ×=

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A Challenge: How hot was the rod? You can use this same equation to take this a step further. Challenge the students to figure out how hot the rod was before it was put in the water. After a few moments of floundering hopefully someone will ask, “What was the mass of the rod?” or more typically “How much does the rod weigh?” Then they will ask, “What is the specific heat of the rod?” Being good teachers, we would never just give them the answers to these thoughtful questions. So off goes Audrey to weigh the rod, and Caesar to look up the specific heat of steel. They come back with the needed information, and now all that is left is some “plug ‘n chug”. This time we are using the equation for the heat transferred out of the metal rod.

CTTC

TTT

T

TshTmQ

start

start

startend

°=−=−°

−=−=Δ

−=−

=Δ

×Δ×=−×Δ×=

34031228

312

3127.7

240011.702400

Q = -2400 calories (This is a negative number because heat was transferred from the rod to the water.)

m = 70 grams, as discovered by Audrey with the electronic balance sh = 0.11— the official specific heat of steel (Thanks Caesar!) First, solve for ΔT. Tend= 28 degrees (This is the ending temperature for both the wa-

ter and rod.) Solve for Tstart. The negatives cancel.

You get a whopping 340 °C!

Another Variation:

If you know the initial temperature of the rod (say you heated it in a thermostat controlled oven or boiled it in 100°C water) then you can have the students solve for the specific heat of the rod. This works well when you don’t know what the rod is made of. And the math is actually easier.


Let’s say 20° CONE REALLY HOT ROD!!!!But HOW HOT????

Perhaps28° C

300 ml

( )

sh

sh

shsh

shTmQ

=

=−−

×−=−×−×=−

×Δ×=

10989.0840,21

2400840,212400

312702400

Q = -2400 calories ΔT = 28-340 = -312°C m = 70 grams Insert the numbers into the equation. Solve for sh (specific heat). You get 0.10989, which rounds to … 0.11. 0.11 happens to be the specific heat of steel. HURRAH!

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Background Information By this time the students should realize that heat travels from a substance of a higher temperature to one that has a lower temperature. They should also know that that beautiful ice covered lake out their doorstep is actually a huge reservoir of heat waiting to escape. If it is summer and the air temperature is warmer than the lake, then heat energy will be absorbed into the water. When, in the winter, the air temperature is cooler than the lake, then we’d expect to see heat loss from the lake. If the loss is adequate, then the water will change states of matter and begin to freeze. Simple enough. However, as the ice thickens, and more importantly, as snow

deepens onto the surface of the lake it provides an insulating layer that re-stricts heat loss or absorption. Thermal conductivity refers to how well heat can be conducted through various substances. A substance that resists the flow of energy is a good insulator and has a low thermal conductivity. Differ-ent materials have different insulating ability. These activities are designed for students to revisit and refine their idea of insulation and to become familiar with the idea of thermal conductivity. They will continue to explore and quantify the thermal conductivity of two substances: steel and aluminum.

Objectives: • Students will understand that heat travels from warmer to cooler temperatures until a state of equilibrium exists. • Students realize that thermal conductivity is a scientific term for the insulating abilities of a given substance. • Students will realize that thermal conductivity refers how well heat can pass through a given substance. • Students will be able to compare the conductive properties of steel and aluminum thus realizing that various substances have different abilities to conduct

heat. (Activity Two)

Description: Activity One In this experiment students will record and compare the temperature changes of water in a Styrofoam cup and glass beaker. Although simple and predict-able, this activity accomplishes a couple things. First, it reinforces the idea that things do not ‘cool down’ but rather heat energy moves from warmer to cooler substances. It also provides the opportunity to use the term ‘thermal conductivity’ to describe their intuitive understanding of insulation.

Materials: per team • Styrofoam Cup

• Glass Beaker

• Thermometer

• Snow or Ice Water

• Hot Tap Water

• Tub

Set Up Styrofoam Cup

Glass Beaker

Snow or Ice Water Equal Amounts of

Hot Water

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Procedure: Activity One

1. Fill Styrofoam cup and glass beaker with equal amounts of warm tap water.

2. Measure initial water temperature.

3. Put into snow.

4. Continue to measure temperature at one minute increments.

Making Sense of the Data:

No surprises here. The Styrofoam container will cool down slower than the glass beaker. But there lies the problem. The students need to think of it as ‘not cooling down’ but rather a slower transfer of heat. In other words, the Styrofoam cup is resisting the transfer of heat into the snow as opposed to the water in the glass beaker which transfers heat at a much elevated rate. Therefore the Styrofoam cup has a lower thermal conductivity than the glass beaker. Thermal conductivity is one of the defining concepts in ALISON. As snow falls on the lake ice surface it acts as a partial barrier to the transport of heat. The ability of the snow to resist the flow of heat is dependant upon the depth and density of the snow pack.

The Math:

Students can use the formula to calculate the amount of heat transferred from each of the containers into the ice water.

Styrofoam Glass

Start Temp (°C)

30 30

End Temp (°C)

22 10

ΔT (°C) End-Start

-8 -20

Volume of water (ml)

200 200

A Challenge: I want my coffee hot! Provide students with a variety of cups, mugs, thermoses etc. Challenge the students to de-sign an experiment that will determine which cup retains thermal energy the best, using the science and math they have learned. They can then write a report that includes their purpose, methods, results and conclusion. This activity evaluates how well students can design a valid experiment AND their under-standing of thermal energy flow.

( )calories 1600

18200−=

×−×=×Δ×=

QQ

shTmQFor Styrofoam Container:

( )calories 4000

120200−=

×−×=×Δ×=

QQ

shTmQFor Glass Container:

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Activity Two: Thermal Conductivity of Two Metals

Materials: (Per Team of Students) • 2+ solid rods 1/2 in X 17 in. Aluminum & Steel. Also try Brass, Copper

(These are usually available at hardware stores.)

• 2 Lab Stands to hold rods

• Candle (NOT birthday candles...they don’t work as well)

• 8+ Thumb Tacks

• 2 Alcohol Burners

• Timing Device

• Steel wool (optional)

Description That done, it is now time to quantify the thermal conductivity of two metals. Students will be heating two rods: one steel and one aluminum. These rods will have a series of thumbtacks fixed with wax at regular intervals (2 cm). As the heat travels down the rod the wax will melt and the thumb tacks will be released. Students will record the release time of the tacks for each rod. This data can be graphed to compare the thermal conductivity of the two substances.

Procedure:

1. Mark rods at 2 cm increments with black marker

2. Clean and rough up rod surface with steel wool and file. (Note: getting the tacks to stick sometimes requires a steady hand and patience. Trust us...it’s worth it!)

3. Melt wax onto thumb tacks… put onto rod before wax cools

4. With alcohol lamps begin heating both rods at same time.

5. Record the time that each thumb tack falls off.

6. Graph and compare. Cool!

Thermal Resistance

05

1015

1 2 3 4 5 6 7 8 9

Tack #

Min

utes Aluminum

Steel

Lab Set Up

Making Sense of the Data Students are able to visually see the heat being transferred down the rods to melt the wax on the tacks. Since the heat travels evenly down the rods (albeit at different rates), the students will soon be able to predict (usually within a few seconds) when the next tack will fall from its position. With this activity students should start seeing the relationship between insulating ability (which we usually apply to substances that help us ‘keep warm’) to a more scientific viewpoint of thermal conductivity. This concept is a key component to ALISON. At this point students should realize that snow does provide a barrier to the conduction of heat. Intuitively they probably realize that the greater the depth of snow the more resistant this layer is to the transfer of heat. Future activities could address the factor of snow density in this heat loss relationship.

Tacks are put on the rod with candle wax. As the rod heats up the wax melts releasing the tack. Comparing the times of the falling tacks provides quantified data to com-pare thermal conductivity of steel and aluminum.

16



Background Information

Students, by this time, should realize that heat is conducted from warmer to cooler substances. Now it is time for them to consider the factors that influ-ence the speed of thermal conduction. One of the factors that influences the speed of heat transfer is the difference in temperature between adjacent warmer and colder substances. The greater this difference, the greater the heat transfer (assuming no other factors are effecting this transfer). This is an experiential concept to most students. Throw one student into a bath of 20° C (64°F) water they would experience perhaps a 5° C tempera-ture difference. It might be chilly, but not terrible. Throw another into a bath of 5° C (42°F) water and, after gaining their senses, will be able to describe what a difference of about 20 degrees feels like. Simply, the heat rushed out of their body at a much greater rate in the colder water. Do this activity often and students will be able to tactilely understand the concept of temperature gradient. Choose the students well and it can become part of your discipline plan. The basic premise of temperature difference is fairly elementary to the forma-tion of lake ice. We can assume that the temperature of the water just below

the ice in a lake would be O°C. Therefore, if the air temperature is below 0°C the conductive heat flow is moving from the lake to the atmosphere. Therefore the lower the air temperature goes below zero, the greater the flow of heat. Ahhh… but if the world were so simple. Other factors come into play as well. Not only do temperature differences determine aggregate conductive heat flow, but also the distance between the temperature readings in a heat exchange system and also the substance through which the heat is flowing through. This is why ALISON averages the air and bottom of snow pack temperatures to provide the temperature difference in the lake/atmosphere heat exchange system. When divided by the average snow depth (which would be the average distance between snow and air temperature readings) we can compute the temperature gradient (the temperature change per centimeter of snow). When combined with the insulating ability of the snow pack, we can get the conductive heat flow streaming out of the lake and making ice.

Objectives: • This activity will reinforce the concept that heat is conducted from warmer to cooler substances.

• Students will understand that the greater the difference in temperatures, assuming no other variables, the greater the heat flow.

• Students will understand although heat is flowing at a greater rate in a higher temperature gradient, equilibrium of temperatures will take longer than in a lesser gradient.

17



Materials (Per Team)

• 1- 1000 ml Beaker (Plastic is best) • 1– 150 ml Beaker (Glass is best) • 2– Thermometers • Tap Water (hot and cold)

(Classroom)

• Crushed Ice (for making very cold water) • Hot Plate and Pot (for making very hot water)

Procedure TRIAL ONE

1. First, determine proper ‘fill levels’ for the two containers. In our experiments this was 500 ml for the larger beaker and 140 ml for the smaller. These measurements will need to remain constant in all experimental trials.

2. Fill small beaker with cold tap water: Measure initial temperature.

3. Fill large beaker with hot tap water: Measure initial temperature.

4. Nest small beaker in larger. Begin timing.

5. At one minute increments, gently stir water in both beakers then record tempera-tures. Continue until temperatures have stabilized within 1 or 2 degrees.

6. Graph results and discuss what has occurred in this activity.

Procedure: TRIAL TWO

1. Prior to Trial Two ask students what would happen if the difference between the initial temperatures was bigger. How would this effect the transfer of energy? Many might say that the slope will be steeper. Inquire further, what about reach-ing equilibrium? Will the duration be a) longer b) shorter c) or the same? Many will feel that the further apart the temperatures are, the faster it will reach equilib-rium.

2. Keep all volumes of water the same but this time use water that has been super cooled (strained through ice… make sure no ice chunks are in sample) and water that has been heated to 60-80°C. Graph results.

Trial 2: Temperature Gradient

010203040506070

1 3 5 7 9 11

M inutes

Tem

p C Hot

Cold

Trial 1: Temperature Gradient

010203040506070

1 3 5 7 9 11

Minutes

Tem

p C Hot

Cold

Lab Set Up Cool

eg 10°C

Warm eg 40°C Direction of

Heat Flow

18


Temperature Differences: Exploring the Rate of Heat Transfer

Making Sense of the Data:

This activity graphically shows that indeed, when the initial temperature difference is increased, the heat flow increased: the hot water cools faster and the cooler water warmed correspondingly . What might be enlightening , but should not be overly sur-prising when one considers the data, is that it took the substances that had a greater temperature gradient a longer time to reach equilibrium. Another way to illustrate this more clearly is to make a chart and graph the temperature difference (ΔT). See chart and graph to the right. If we were to cut and paste the slope of Trial 1, it would fit perfectly with the slope of the second trial.

Comparing Temperature Differences

0

10

20

30

40

50

60

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Time (minutes)

Tem

pera

ture

C°

Trial 1

Trial 2

Making the Application:

Depending on local conditions, the effects of temperature difference should be easily ob-served at your site. If the snow depth and density are the same, ice should form at a faster rate when the air temperature is –20°C (with a 20° temperature difference) than if it is –5°C (5 ° difference). This concept in place, one would expect the areas with consistently lower temperatures to have the thickest ice… ahh but there is more to it than temperature difference...as we will soon see!

A Challenge: Myth or Fact—Does cold water really boil faster than warm water? Does warm water freeze faster than cold water?

A nice closure task could be to ask the students if it is possible for cold water to boil faster than warm water, and also, can warm water freeze faster than cold water? They should use the data from this activity to support their claim. Then for homework ask them to bring in more evidence to support their reasoning. Their evidence can be from asking an expert, doing an experiment or using internet or paper resources. You think you have it figured out? Not so fast, cowboy! It seems this topic isn’t as sim-ple as we first thought. Before you go any further … check out the Mpemba Effect.

(Swanson Note: Yeah, I didn’t believe Abbott at first either…. But check it out! Had to do some back paddling with my students!!)

Time Hot Cold ΔT 1 38 12 26 2 36 18 18 3 35 21 14 4 34 24 10 5 33 25 8 6 32 27 5 7 32 28 4 8 31 28 3 9 31 29 2 10 31 29 2 11 31 29 2

Time Hot Cold ΔT 1 58 4 54 2 50 12 38 3 48 18 30 4 46 24 22 5 44 27 17 6 42 31 11 7 41 32 9 8 40 34 6 9 40 35 5

10 38 35 3 11 38 36 2 12 38 36 2 13 38 36 2 14 38 36 2

Trial 1 Trial 2

19



Background Information: This activity is an extension of the temperature difference activities and as a discrepant event leading into latent heat. The experimental design is essen-tially the same as the previous lesson on temperature difference. It merely spreads the initial temperatures until the cold substance is actually 0°C (ice) and the hot water is near boiling. In the previous lesson, when we spread the initial temperature difference fur-ther apart (in our example 54° C), it caused an increasingly steeper heat trans-

fer. The hotter water cooled and the cold water warmed quicker than in the instance where the temperature difference was less (26°C). Now we will increase the initial temperature difference to 70°C . If our results were to be consistent with our past experience we would expect to see even a steeper curve suggesting a faster exchange of heat energy. What we get, however, may be a bit more perplexing.

Objectives • Students will graph results of heat transfer and compare these with previous temperature difference experiments. • Students will understand that heat is being conducted into the ice by evidence of the change of hot water temperature. • Students should realize that although heat is being transferred into the ice, this is not a corresponding change of temperature of the ice. • Students will begin to realize that it requires energy to change a state of matter with no temperature gain.

Description of Activity Students will set up a similar activity to the previous temperature difference experiments. The only change is that in this experiment the lower tempera-ture will be frozen ice. Like the last experiment, students will take tempera-ture readings at regular intervals but for a shorter length of time (3 minutes

should suffice). At the end of the experiment students will be able to com-pute the amount of calories exchanged between the hot water and the ice. They will realize, after computing heat loss in hot water and comparing this with the temperature gained in the melted ice, that the numbers simply do not jive.

Materials (per team) • 1– 1000 ml beaker or tub • 1– paper or plastic cup • 2—thermometers • 1– graduated cylinder

For Classroom • Freezer or a very cold door step • Hot plate with pot for heating water. • Drill with 1/2 inch drill bit

Lab Set Up

Hot Water With

Thermometer

ICE

Hole Drilled in Ice and Filled with Cold Water and Thermometer In-serted

20



Procedure:

The Day Before

1. Measure a set amount of water, put into paper/plastic cup (glass beaker might break during freezing).

Class Time

1. Drill a hole into the ice (do not go all the way to the bottom). See drawing to the right.

2. Put a bit of cold water into test tube. This will cool down to the ice temperature but should not freeze.

3. Pour a predetermined amount of hot water into a 1000 ml beaker. This should be around 70°C. Measure temperature and record.

4. Measure and record initial temperature of ice. Determine the temperature difference be-tween the two measurements and compare with past experiments.

5. Nest ice cup into hot water beaker. Record both temperatures and note changes every 30 seconds.

6. After 3-5 minutes stop experiment (In order to prove the point of the discrepant event, ice need not have melted fully nor do the temperatures need to reach equilibrium.)

7. Graph results of temperatures and compare with previous experiments.

Making Sense of the Data In this particular trial a total of 5000 calories (ΔT x Volume = 10 °C x 500 ml) were transferred from the hot water to the ice. That being true we would expect a significant temperature change in the ice. This did not occur although much of the ice began to melt. With this observation students might real-ize that although there was not a corresponding temperature change, perhaps the heat was necessary to change the ice into liquid water (latent heat) — perhaps an ‘ah ha!’ moment. With this understanding , the students will now be ready to go onto quantifying the latent heat re-quired for a change of phase.

A hole needs to be drilled to fit the ‘ice’ thermometer. A 1/2 inch drill bit should do the trick (make sure there is plenty of room to fit ther-mometer.)

0 1 2 3 4

Minutes

Tem

pera

ture

0 1 2 3 4

Minutes

Tem

pera

ture

0 1 2 3 4

Minutes

Tem

pera

ture

Water

Ice

21



Background Information If students have done the activity “Spreading the Temperatures: Exploring Latent Heat” then they realize that something fishy is going on with the stan-dard conception of 1 calorie is equal to 1°C temperature gain/loss per 1 gram of water. In the experiment, the heat was released from the hot water, pre-sumably into the ice (which gradually melted) However, there was no corre-sponding change in temperature.

Therefore, the students probably already sus-pect that a greater amount of energy is required to make the hard stuff into liquid.

Ahhhh, but the devil is in the details. How much energy is required? In order to break the molecular bonds to change a state of matter (from solid to liquid, or liquid to gas) does re-quire vast amounts of energy. If we were to put a kettle of ice on the hot stove, it would take a bit of time but the ice would eventually melt into liquid water. However, although heat is being absorbed into the ice (and thus causing it to melt) there would not be a corresponding rise in tem-perature. This is called latent heat… the energy required to change the state of matter. In order to melt a gram of ice requires 80 calories of energy to be absorbed. In order to change 1 g of water from liquid to a gas (without any change in

temperature remember) takes 540 calories! (A greater number of calories are required to transform water to vapor as greater inter-molecular forces must be overcome in the liquid-to-vapor transformation.) So why is this important to ALISON? If ice must absorb 80 calories per gram of water to become a liquid then the inverse is true… 80 calories per every gram of lake water needs to be released in order to become ice. There-fore, although your study lake may be getting colder and colder in the au-tumn days, it requires a huge exchange of heat to finally begin growing ice. We’ve all experienced the ‘autumn wait’. The temperature may be bitter cold yet the lakes and rivers refuse to freeze tight. Day after day we wait with skates and snowgos close at hand, wondering how the lake or river could be so oblivious to the cold temperatures. Yet, unseen by us, vast amounts of energy are being released. It isn’t until the latent heat has been transferred sufficiently that ice growth can occur. But when this latent heat has been released, the transformation is abrupt and swift. The ice forms and thickens quickly. Within days the ice might be safe to cross. But how much energy is required? We could just tell them it requires 80 calories to convert a gram of ice into water with no gain of tempera-ture…..or they could figure it out themselves…….like good little science stu-dents.

Objectives:

• Students will be able to maintain strict experimental design in order to limit the variables that would affect successful data. • Students will determine from drop in hot water temperature the exchange of heat in calories (or joules). • Students will recognize that the increase (if any) of temperature in the ice/ice water does not fully account for the energy transfer. They will understand

this ‘lost heat’ is actually the latent heat necessary to achieve a phase change— from a solid (ice) to a liquid (water) without a corresponding increase in temperature.

• Students will use acquired data to accurately compute the amount of heat required to change 1 gram of ice into 1 gram of water with no apparent change of temperature.

22


Description of Activity Students will be nesting a container of ice into a hot water bath. The heat will be transferred from the hot water to the ice resulting in the gradual melting of the ice block and the reduction of temperature in the hot water bath. Students will use the volume of the hot water and the resulting reduction of tempera-ture to determine the transfer of heat in calories. By measuring the volume and temperature change of the ice water, students will be able to compute the amount of energy required to achieve this temperature change. The students will be confronted with a large number of missing calories that cannot be ac-counted for in temperature gain… this is the latent heat required to change a state of matter from ice to a water. Assuming the data are clean, students should be able to compute the latent heat required to achieve the phase change from a gram of ice to a gram of water (80 calories).

Materials (for Each Team)

• 1– Tub

• 1 1000 ml Beaker (filled with 50ºC hot water)

• 1 Paper Cup (previously filled with water and frozen)

• 1- Thermometer

• Lid for beaker (a large petri dish works)

• Poly fill or other insulation material

• Stirring spoon


Possible Data Sheet:

Hot Water: Volume = ________ Beginning Temp = ______ Ending Temp = _______ Cold (Ice) Water: Beginning Temp = _____ Ending Temp = ______ Volume = ______ Mass = ______ Remember: 1 ml of water = 1 g of water

Procedure

Prior to Activity: 1. Freeze water in cup. For our purposes, we will say it is 250 ml of water to be

frozen. 2. Due to the freezer, the temperature of the ice will likely be below zero and difficult to quantify. If so bring ice

cup out a few minutes prior to beginning activity. Putting ice in refrigerator for a short while will allow tem-perature to rise to zero.

During Activity: 1. Measure out a set volume for the hot water. Volume should not be so much as to float ice cup. 2. Put hot water beaker into a tub that is insulated (heat loss must be minimal). We used polyfill although other

substances would work as well. 3. Measure beginning temperature of hot water. 4. Put cup of ice into hot water. Cover with a lid (large petri dish, piece of cardboard, whatever) and cover with

other insulation. 5. Give it about 4-5 minutes, then check. The ice should nearly be melted. 6. Take the ice cup out of the hot water bath. Stir hot water to fully mix. Take temperature (this is the ending

temperature of the hot water.) 7. Stir ice/water to melt any remaining ice. This will mix the water and bring the temperature down to near 0°C. 8. Measure volume of resulting ice water. 9. Do the math. See next page.

Poly FillInsulation

ICEICE

Hot Water– Perhaps 50° or more.

Hot Water– Perhaps 50° or more.

Petri Dish LidLab Set Up

23


Making Sense of the Data If all’s gone well with the experiment, then the students will be able to use their acquired skills and data to figure out the ‘unaccounted heat exchange’ that is necessary to change water from a solid to a liquid.

[ΔTH (MH)] - [ΔTC (MC)] MC

Latent Heat=

ΔT= Temperature Change

M= Mass (1 ml = 1 g H2O)

H = Hot Water

C= Cold Water

THE FORMULA


Hot Water BeakerVolume: 388mlBegin Temp: 50°CEnd Temp:22°CΔT:28°C

‘Ice Water’ CupVolume: 120 mlBegin Temp: 0°CEnd Temp:9°CΔT:9°C

SAMPLE DATA

First Figure the Temperature Change (ΔT) for the Hot Water

Begin Temperature — Ending Temperature of Hot Water Bath

50° - 22° = 28° (ΔT)

Compute Calories For the Temperature Increase of Ice Water

Ice Water Volume x ΔTc

(ΔTc = Ending Temp – Beginning Temp of Cold Water)

120 g X (9° - 0°) = 1080 Calories

Now Sleuth Out Number of Calories Not Accounted For

Calories exchange—Calories for temperature increase of ice water

10,864 calories—1080 calories = 9784 calories missing in action.

These ‘missing’ or latent calories were necessary to accomplish the phase (but

not temperature) change.

Now Figure the Latent Heat Per Gram for Phase Change .

Unaccounted Calories / Volume of Cold Water

9784 calories/ 120 g = 81.5 calories per g

That’s pretty darned close to the 80 calories per gram needed

for this phase change!

Volume of Hot Water x (ΔTh)

388 g X (28°)= 10,864 calories released from hot water bath

Then Determine the Amount of Energy Transferred in Calories

NUMBER CRUNCHING STEP BY STEP

24



The MEGA Challenge: Predict the volume of water in this cup … with latent heat.

Once students get the idea that the amount of energy transferred during a phase change and between phase changes is a predictable number, they are ready to put their knowledge of heat transfer to the test. Here is the scenario. Teachers freeze a known amount of water in paper cups. But don’t tell the students how much water/ice is in the cup. That is for them to figure out! Students can use the same set-up as they did to verify the latent heat of fusion (80 cal/g). They record the temperature and amount of warm water. They place the cup of ice in the warm water until the ice is almost completely melted. After the melted ice is re-moved from the warm water the final (or ending) temperatures of both the warm and cold water are recorded. This data, plus the knowledge that it takes 80 cal/g to melt ice into water and some basic algebra skills are all that is needed to mathematically figure out the volume of ice in the cup.

Warm Water

Cold Water/Ice

Start Temp (°C)

50 0

End Temp (°C)

22 9

ΔT (°C) End—Start

-28 9

Volume of water (ml)

388 ??

ml 122 grams 12289864,10

809864,10864,10

===

+=+=

+=

mm

mmQQ

QQQlc

lcw

There was no phase change for the warm water, so this is the total number of calories transferred. For the ice there was the number of calories needed to change the ice to liquid water (latent heat) plus the number of calories needed to raise the temperature from zero to 9 degrees Celsius. Then you just insert the equations for Qc and Ql. Solve for m, and you get the mass of the ice. Because 1g = 1ml of wa-ter, you now know the volume of water in the cup, without measuring it. Amazing.

After a student has submitted their prediction for the volume of water in the cup there are two ways they can check their answer. First, they can grab a handy graduated cylinder and measure the amount of melted ice in their cup. Second, they can beg their teacher to tell them the original amount of water that was frozen into the cup. A percent error can be calculated for both methods. Then ask them to give some possible explanations for why there was error (evaporation, sublimation, water cohesion, spillage, etc.).

Latent Heat Transfer:

80×= mQlThe latent heat for freezing is 80 calo-ries per gram.

Heat Transfer For Warm Water:

( )calories 864,10

128388=

××=×Δ×=

w

w

w

QQ

shTmQHeat Transfer For Cold Water:

mQmQ

shTmQ

c

c

c

919

=××=

×Δ×=

?

25



Background Information The concept of thermal conductivity may be new to the students. However, it is just a way of describing the insulating ability of a given substance. Goose down has a low thermal conductivity or a high thermal resistance… it doesn’t allow heat to pass through as quickly as, let’s say, a suit of wet cot-ton. The goose down has greater insulating abilities thus making it a better substance for making a warm, winter coat. This principle is probably intui-tive for most students (although adolescences do not necessarily translate this into making wise clothing decisions in the middle of winter), but it may be more difficult to quantify the concept in a meaningful way.

This experiment seeks to monitor and quantify the movement of heat through two different substances with different thermal conductivities. It allows stu-dents to better conceptualize how temperature readings will vary as heat moves through various substances. Once students understand how monitoring temperature can provide insight to heat movement, they will be better equipped to analyze the temperature data derived from their ice monitoring site. In turn, they will have a better under-standing of the conductive heat flow from their lake, through the ice and snow, and into the atmosphere.

Objective: • Students will realize that temperature can provide information about the direction and amount of conductive heat flow. • Students will understand that various materials (with various densities) have different thermal conductivities. • Students will use temperature measurements to compare the conductive heat flow of two substances. • Ultimately they will be able to apply this conceptual understanding to why Project ALISON gathers certain temperature measurements.

Materials: Per Team: • 2- 1000 ml Glass/Plastic Beakers • 2- plastic vials w/ caps (75 ml is what we used) • 4- thermometers—1 degree accuracy or better • variety of insulating materials: we used table salt and wood chips (from animal bedding) • Large tub (dish washing tub works) • Snow • HOT water (best to heat to 80C or so)

SALT

Wood Chips

Hot Water

SNOW

Lab Set Up

Description of Activity Students will be creating a system of conductive heat flow through two substances (wood chips and salt). They will monitor and analyze the temperature readings as heat passes through these substances. Using this data they will hypothesize which system transported the most heat. This will be confirmed by pre and post temperature readings a given distance from the heat source (the hot water in the vial).

NOTE: Salt and wood chips are two suggested sub-stances that will have different rates of heat flow, but others may work just as well.

26



Procedure: 1. Put beakers of salt and wood chips into the tub with snow. Make sure the snow is filled to the same level as the chips and salt. Allow these to set for a few

minutes for the temperatures to stabilize. 2. Heat water (80+ degrees C)… put into vials. Measure starting temperature of vials and record. 3. Place vials into the wood chips and salt. Make sure these are buried deep and equally. 4. Push thermometers down halfway into salt/wood chips. One should be close to the outside wall of vial…one should be close to the inside wall of the glass

beaker. 5. Measure temperatures in 1 minute increments. This should continue for about 15 minutes. 6. Look at data to discern which vial lost the most heat. 7. Take and record ending temperature of vials. Compare this to the first temperature reading to determine which indeed lost the most heat.

Making Sense of the Data

Before students have a chance to find the ending temperature of the vials, it might be a good idea to analyze the data in terms of heat flow. The graphs (to the right) show a sample of what the students might expect for data. The data suggests that salt has a higher thermal conductivity than the wood chips. The heat passes through the salt at a faster rate than the wood chips. This accounts for the data that was acquired. The salt has a lower inner temperature than the wood chips. This may at first seem a paradox as the outer temperatures are the op-posite: the outer temperature of the salt was significantly higher than that of the wood chips. In terms of heat flow, the students should conclude that the heat is traveling through the salt at a greater rate (thus raising the outer temperature). The wood chips had a lower thermal conductivity or greater insulating ability, trapping the heat closer to the heat source.

SALT

05

10152025

1 2 3 4 5 6 7 8 9

Time (minutes)

Tem

pera

ture

(C)

Inner

Outter

Wood Chips

05

10152025

1 2 3 4 5 6 7 8 9

Time (minutes)

Tem

pera

ture

(C)

Inner

Outter

SaltTemperature Change of Vial

020406080

100

Wood ChipsTemperature Change of Vial

020406080

100

27


Designing the TWITT: Maintaining Experimental Design

Background Information: The lessons are done… the weather’s becoming colder. The students are bit-ing at the bit. They are now ready to become professional cryologists (Pay may not be so hot but the benefits are cool!) All they need is some lake ice. Before they set up of the ALISON observatory, why not let the students have a crack at designing the experimental protocols for the observatory? They should know by now that the purpose of ALISON is to measure the conduc-tive heat flow from the lake into the atmosphere. They know that the tem-perature gradient will influence the direction and the magnitude of heat flux between the lake and atmosphere. They know a layer of snow has an insu-lating effect and, depending on the depth and density, will have a varying resistance to the conductive heat flow. Finally, they know that the develop-ment of lake ice is a critical component to the entire project as the growth and decay of ice is a barometer for heat transfer. So let them have a crack at it. Students should already understand the ele-

ments for an effective experimental design. They should realize that vari-ables must be eliminated or accounted for. They should realize that data and procedures must be consistent and easily replicated. Provide the students with the task of designing the ALISON observatory and protocol. Have it culminate with the development of the TWITT (Thermal Wire Ice Thickness Thingy) design. Depending on the age level, it may not be as important to create an alterna-tive (or replica) of the TWITT as it is to design a methodology and then dis-cuss its shortcomings according to effective experimental design. For in-stance creating a measuring rod that works through a hole drilled in the ice is fine as long as the students realize that such a protocol would cause distur-bance of the ice and snow in the area and would require the scientist to change his study area with each visit.

Objectives: • Students will develop the types of data necessary in order to compute the conductive heat flow in a lake system. • Students will determine what measurements and equipment are needed to obtain this data. • Students will develop a device that will accurately measure lake ice thickness. They will discuss the shortcomings of their device and protocol in terms

of impacted variables and data accuracy.

Description of Activity: Tell the students that they have been given a multi-million dollar grant to measure conductive heat flow from a nearby frozen lake. It is up to them to de-velop the experimental protocol for this project. They will need to collaborate with their team of scientists in order to develop the methodology and equip-ment necessary to extract the cleanest data. In addition, they need to develop a device to measure ice thickness. Although this device may be crude and sim-ple, what is most important is: a) accuracy to the nearest tenths of a centimeter and b) limiting (or at least recognizing) the variables that would affect the accuracy of this experiment.

28


Story Time With Swanson: My class of 6th graders seized on this project with a vengeance. At first most inventions re-quired the drilling of a hole into the ice (this was fine as long as they realized how this affected the data and the study site for future measurements.) But that wasn’t enough for some….they wanted to figure out the real TWITT. Soon the chalkboard was filled with ideas. Some tried ideas that didn’t disturb the snow but still drilled a hole through the ice. Some came up with improbable buoys that somehow rested under the ice sheet. Then one boy came up with an idea of a premeasured rope with a weight on the end. Somehow the rope would be released from the icy grip and pulled up until the weight hit the bottom of the ice. Then it was a simple matter to

measure and subtract from the original length. But how to release the rope? Then it became a feeding frenzy. They knew they must be onto something big...perhaps it was the look on my face. At some point I showed the class a bit of steel wool and a battery. When the current was sent through the steel wool it became hot and burned. We’d done a bit of electricity unit so they had an idea of elec-tron movement and it was easy to teach a bit about resistance wire (an easy application would be their toaster.) Now the race was on….but alas the class period was over. It was time to go home. The next day Holly handed me a piece of paper. On it was a drawing of a TWITT. It was a job well done.

Designing the TWITT: Maintaining Experimental Design

Making Sense of the Activity This lesson has three tasks really. Part one is for the students to decide what measurements are necessary to determine the heat flow from the frozen lake. By this time they should realize that ice thickness, snow depth, snow density, air, snow, and water temperatures are critical components to understanding the heat exchange at a lake. The second part is for the students to decide how they can accurately obtain these measurements given that these can vary over the surface of the entire lake. The third part… and perhaps the most fun… is developing the TWITT (Thermal Wire Ice Thickness Thingy). There are numerous ways to measure the lake ice thickness. What is important is not necessarily the device, but understanding the limitations (the unintended introduced variables) which would be in-herit in their invention.

29



Background Information Up to this point, this booklet has provided ideas of how to translate the central concepts of ALISON into a classroom setting. This is all well and good. However, during the course of the year, students will be gathering real data that can be displayed, analyzed, and compared in many different ways. After all, it is analyzing the ALISON data that keeps Martin busy all year around. Guiding the students through the process of analyzing data is not only a vital part of the scientific process, but it allows for a learning

experience in problem solving, creative and divergent brain power, and the opportunity for students to think outside of the box. Analyzing the ALISON data provides nearly unlimited possibilities for students of any age level— it is only limited by the imagination and inspiration of the individual teacher. We’ve included some sugges-tions of how the data might be analyzed. This is certainly not an ex-clusive list, but rather one that might spark new dialogue and ideas from other teachers.

Objectives • Students will graph and compare data from three observatories in three climatic regions to compare ice growth and snow depth. • Using the same data, students will develop a different graph that compares not just thickness but differences in ice development. • Students will develop a valid hypothesis, based on available data, and understanding of climatic differences, that explains anomalies in data.

Description of Activity The data that are used for this activity were from Denali and Seward for the winter of 2003-4. Although the data are not complete, they provide an example of how a set of data can be displayed in a number of ways to provide interesting interpretation.

Denali Date Snow L1 L2 Ice Depth 14-Nov-03 2 100 113 27

26-Nov-03 20 100 104 36

4-Dec-03 16 100 84 56

18-Dec-03 14 100 72 68

Seward Date Snow L1 L2 Ice Depth 18-Dec-03 16 97.9 100.5 41.6

23-Dec-03 21 98.4 100.9 40.7

2-Jan-04 10 89.4 98.6 52

7-Jan-04 10 88.6 98.4 53

10-Jan-04 41 89 98.6 52.4

14-Jan-04 33 87.9 99 53.1

22-Jan-04 15 88.3 98 53.7

29-Jan-04 13 78.7 98.6 62.7

12-Feb-04 4 73.5 97.5 69

18-Feb-04 0 64 97 79

Sample Data: To the left is a sample data set from Seward and Denali. The data is only displaying the date, ice thickness, and snow depth. Although not complete, it provides some interesting insight. At first glance, one might not discern much is happening other than it snows way too much in Seward and that ice in growing rapidly at both sites.

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Graph A: Ice Thickness

Making Sense of the Data: At first glance, although the dates suggest a much earlier ice formation in Denali, growth rate seems to be fairly even with the ice in Denali formed sooner. Students might no-tice that Denali’s ice growth was more even than that of Seward. But without further data it would be difficult to determine if this growth was significant or conclude any pos-sible causes. So let’s add snow load to the graph…...

Denali Ice Growth: 2003-4

020406080

100

11/14

/2003

11/21

/2003

11/28

/2003

12/5/

2003

12/12

/2003

Seward Ice Growth: 2003-4

020406080

100

12/18

/2003

12/25

/2003

1/1/200

41/8

/2004

1/15/2

004

1/22/2

004

1/29/2

004

2/5/200

42/1

2/200

4

Hmmm….some pretty crazy snow in Seward By putting snow into this graphic illustration of ice growth, students might conclude that there seems to be an inverse relationship between the depth of the snow and the growth of ice. When the snow is deep, the ice growth seems to even out. When the snow layer thins, the ice thickness increases. Student might conclude this has to do with the insu-lating properties of snow. Indeed this would corre-spond with the lessons of heat conductivity that they have been learning. However, by displaying the same data a different way, an entirely new trend emerges.

Denali Snow and Ice

11/1

4/20

03

11/2

1/20

03

11/2

8/20

03

12/5

/200

3

12/1

2/20

03

Ice Thickness

Snow Depth

Seward Snow and Ice

12/1

8/20

03

1/1/

2004

1/15

/200

4

1/29

/200

4

2/12

/200

4 Ice Thickness

Snow Depth

Graph B: Ice Thickness and Relative Snow Load


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0

20

40

60

80

100

120

Denali Ice GrowthL1- L2- Snow Load

0

20

40

60

80

100

120

L2

L1

Snow Load

40

60

80

100

120

Seward Ice GrowthL1-L2- Snow Load

0

20

40

60

80

100

120

Snow Load

L2

L1L1

Now we’ve taken the same data and, after a partially successful attempt at using Excel to display this data, graphed the L1 / L2 measurements and the relative snow depth on top of L1. We’ve graphed the data outward from 120 so that as the L1 and L2 measurements changed, the graph would visually simulate growth of the ice. By doing this we can now see that the Seward ice grows much differently than does the lake ice in Denali. The Denali ice becomes thicker by growing downward. (This is what one would expect.) But alas, things are different in Seward-ville. Once measurements were started (about 3 weeks after ice formed on Bear Lake) the ice did not become significantly deeper. The thickness of the ice occurred because of successful ice growth ON TOP of past ice. Hmmmm… per-haps to someone in the Interior this would make little or no sense. But by putting snow load into the comparison we get a partial understanding of what is go-ing on. Seward experienced several large dumps of snow. In the most significant, there was over 40 cm of snow on top of the lake ice. During this time the ice experi-enced little thickness change. Then the snow went through a thawing and consolidation stage resulting from cracks in the lake ice, warmer weather, and ther-mal conduction from the lake water. The snow ended up as thick overflow, which quickly froze into the next successive layer of ice. The point is this: ALISON provides a wealth of data that can be analyzed in many different ways that would be appropriate for a wide range of age levels of stu-dents. This is the beauty of ALISON. It is only up to the teacher’s creativity to provide for a unique and valuable learning experience for their students.


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Unlocking the Invisible Ice Crystals

Background Information We’ve all heard the expression that no two snow flakes look alike. Indeed the exhaustively thorough and if not a bit idiosyncratic work of Mr. Bentley photographically verifies that indeed no two snowflakes are identical. However, the formation of the crystals do follow predictable hexagonal patterns. As a result of the shape of the hydrogen/oxygen bonds, when water molecules are fused into ice crystals they form along two different axes: the C axis which is a single polar axis, and the A axes which are six equally spaced rays spreading out. This is what give the snowflake (and ice crystals) flat, hexagonal appearances. “So what?!” you ask. What does this have to do with lake ice? Hold on for a moment. Lake ice can be classified into two types: congelation ice (known also as “black ice”) and snow ice (also known as ‘white ice.’). The congelation ice is the wonderfully clear ice that forms at the bottom of the lake ice. Snow ice is formed when snow mixes with water at the top of the ice cover and freezes. This ice has an opaque or white color due to the high concentration of air mixed in with the ice crystals. By obtaining ice samples from the lake, we can get a better understanding of the various layers that occur when lake ice grows. Also, given a good sample of congelation ice and a set of polarizing filters we can see the otherwise invisible world of growing ice crystals as they compete for space. It’s guaranteed to solicit some ’oohs and ahhhs’ from the students and, who knows, perhaps some real building of dendrites within the gray matter.

C Axis

A Axes

Materials: Note- This is an outdoor/classroom activity lead by the teacher. It requires specialized equipment for best results (namely the ice corer). If this is not available, experiment with other methods to acquire or make an ice sample (chainsaw, freezing water in PVC or on a cookie sheet, etc). It’s definitely worth the effort.

• Ice corer

• Band Saw

• Polarizing Filters (These are available through school scientific catalogs.)

• Light Table (or simply try upturned fluorescent light or the sky — this protects electronics from melting ice!)

Procedure:

Obtaining Sample: If you are fortunate enough to buy, steal, beg, or oth-erwise obtain an ice corer then this part is easy. Oth-erwise you will have to experiment with a chain saw or other technique. Good luck.

If you are able to get a clean sample, lay the ice core out to examine the various layers of ice growth. Try to match this ice growth with records from ALISON site and weather data. Check out the photo of Martin with ice from the Poker Flats Pond. The top layer of snow ice is easily discerned from the bottom conge-lation ice.

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Slicing Sample: In order to view the individual crystals a sample of congelation ice must be cut to a thickness of 1/4 inch. First, from your ice core, cut a 6-12 inch seg-ment from the congelation ice layer.

If using round core sample, cut a 6-12 inch length. Then di-vide the core lengthwise ex-posing a wide face of flat ice.

1st

2nd Now cut a thin slice (about 1/4 inch). This slice will become the ice sample to examine.

Band Saw Blade

Ice Core Sample

(End View)

3rd Take two sheets of polarized plastic and put the thin ice sample between them. If crystals do not show up, then try rotating the top polarized sheet 90 degrees.

You might get a sample that looks something like the photo to the left. The long striations are individual congelation ice crystals. You will note that at the top there are many small ice crystals - this is granular snow ice. As the underlying congelation ice grew thicker, the crystals grow larger and become less numerous. The larger, slower growing ice crys-tals have parallels with igneous rocks: fast cooling = small crystals; slow cooling = large crystals.

If you didn’t get the nice view of elongated crystals - known in the trade as a columnar texture - don’t fret. The colum-nar texture indicates that the c-axis of the ice crystals is oriented in the horizontal direction. But congelation ice doesn’t always grow this way. Sometimes the c-axis is ori-ented in the vertical direction and the crystals are some-what amorphous and featureless, like mashed potatoes. Scientists are not sure what causes the different align-ments of the c-axes. Nor do they know why the axes can suddenly change. However, if you did not get the way-cool elongated crystals, then try a different segment of ice core or an ice sample from a different place in lake. You may end up with better results.

Unlocking the Invisible Ice Crystals

PolarizingFilter

Thin Ice Sample

Polarizing Filter

LIGHT BOX

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How Much is it Worth?

Background Information: At the end of a good day of data collection, crunch the numbers right and you’ll end up with a value for conductive heat flow. Let’s say you get –8.766 W/m2. That’s a respectable heat flow. Nothing to be ashamed of. But how do you know that? Most of us have no idea what that number means. Do some comparing and you’ll see that Barrow pulls in conductive heat flows of around –20 W/m2.

Most CHF’s (Conductive Heat Flow) are negative until spring arrives, although Wasilla has been known to sport a positive heat flow during a warm snap in the dead of winter. This lesson is designed to make the CHF value more meaningful to students. By converting your CHF into a monetary value, you’ll be sure to grab their attention. “Money is good!”

Objectives: • Students will compute metric and non-metric conversions. • Students will discuss how conductive heat flow changes throughout a 24 hour period and throughout the year. • Students will compare how conductive heat flow values vary at different locations around the state. • Students will distinguish between low quality and high quality energy.

Description of Activity: This activity is mostly a paper/pencil worksheet with multiple opportunities for discussion. First the students calculate how much heat, in Watts, is being trans-ferred from the entire lake into the atmosphere. Then they determine how much money an electric company could collect if they could gather this energy and sell it in the form of electricity. Finally, the students discuss why, ultimately, this is not possible.

Materials: • A conductive heat flow value from your lake—values from two or three different days is

handy, the bigger the difference, the better. • The area of your lake If someone hasn’t already done this for you it can be estimated from a topographic map or measured in the field. Any units will work, acres, square miles, square feet, etc. Just adjust your conversions accordingly.

Procedure: Nothing tricky here. Let the student’s work through the calculations. They may need more or less assistance based on their math skills. After they’ve done the calculations it’s time to check for accuracy and then discuss.

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How Much is it Worth?

HOW MUCH IS IT WORTH?

Goal: If you could collect the energy that is flowing from the lake into the at-mosphere and turn it into a usable form (electricity), how much would it be worth? Step 1: How big is Lake Lucille in m2? Lake Lucille is 362 acres. One acre is 4047 m2. SHOW YOUR WORK. Step 2: The heat flow out of the lake on December 24, 2004 was -8.77 W for each square meter. How much energy is flowing out of the whole lake? SHOW YOUR WORK. Step 3: Change your answer from W to kW. (1000W=1kW) SHOW YOUR WORK ** The negative value indicates a loss of heat from the lake into the atmos-phere. A positive value would mean heat was flowing into the lake. At this point the negative sign is eliminated for simplicity. Step 4: The electric company charges $0.08828 per kWh (kilo-watt-hour). If the electric company could collect the energy and turn it into electricity, how much money could they make per hour? SHOW YOUR WORK. The temperatures at the lake are constantly changing. So the heat flow is changing too. Use the heat flow values below to calculate the monetary value of the energy on the dates listed below for Lake Lucille.

December 15, 2004 = 0.3 W/m2 February 7, 2003 = 13.1 W/m2

Is it realistic for the electric company to do this? Explain your answer.

362 x 4047 = 1,465,041 m2

1,465,014 x -8.77 = -12,848,172 W

-12,848,172/1000 = -12,848.2 kW

12,848.2 x $0.08828 = $1,134.24

$38.80

$1,694.24

Making Sense of the Data: “$1000 an hour!” The students can hardly sit in their seats. Then we start discussing why nobody is harnessing the great powers of conduc-tive heat flow from lake ice. Their dreams of wealth slowly fade. But it isn’t an easy process. They struggle. When asked why it isn’t being done their initial answers are good (“it’s private property”) but not based on the laws of thermodynamics. The problem is with capture and transfer. How can you contain 8 Watts per square meter? And if you could, how would you convert it to a usable form of energy, such as electricity? This is prime time for a discussion of high quality energy and low quality energy. High quality energy is concentrated and can perform useful work. An example of high quality energy is fossil fuels. Low quality energy is dispersed and cannot perform useful work. Conductive heat flow from a lake is an excellent example of low quality energy. Another example is the heat stored in the ocean. The quantity of energy stored in the Atlantic Oceans is greater than all the oil deposits of Saudi Ara-bia, but because it cannot be gathered and put to work, it is useless. Useless? Really? Well, only in a monetary way. Good scientists care about more than money, right? Good scientists care about issues such as climate change and global warming. And that is where our little lake ice project fits in. Those 8 W/m2 may make a huge difference in our climate. Before ALISON no one knew how much energy was en-tering the climatic system from frozen lakes. Now we are document-ing this variable and we can look for changes as the climate changes. Doesn’t sound so useless anymore, huh?

Documents

ALISON Guide to Heat and Energy Activities for the … Guide to Heat and Energy Activities for the Classroom Marc Swanson (Seward Elementary, retired) Cheryl Abbott (Wasilla High School)