Convection Unit
Essential Question: “Does convection occur in all states of matter; solids, liquids
and gases?”
Grades: 6-9
Time: 4-6 class periods
Objectives: Students will follow procedural steps, conduct experiments, make observations,
write explanations, collaborate with partners to develop a claim, identify evidence that can be
used in development of scientific argument, closely read text for relevant information,
construct a scientific argument. The content is also related to Plate Tectonics, weather, ocean
currents, energy conversions, density in fluids, molecular movement, diffusion and other topics.
No background information is needed. Students will explore and read to uncover necessary
concepts and learn new vocabulary.
Teacher Preparation:
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Read all experiments and carry them out yourself to determine any needed adjustments
that should be made.
Copy the student sheets and the close reading material (to be done after labs).
Make a chart or handout of any close-reading annotations you want students to use.
Gather sufficient quantities of all materials and store in easy to access containers for
each experiment. Items should be available at local stores.
Provide instruction on safety precautions before and during the unit.
Engagement: Show students a picture or short video of a hot air balloon. Ask if they
have ever thought about going up in a balloon. Briefly discuss. Tell them that you will
be conducting some investigations that help explain how balloons and also some
natural processes work.
After Lab 1-2: Ask groups to decide on a position related to the EQ and prepare a poster chart
outlining the evidence they have gathered so far.
Alternative: Ask them to discuss the EQ, with each student listing information related to the
findings. Afterward each student can individually write an argument essay.
Assessment: Provide the following RAFT scenario. Students will write a letter explaining their
ideas to the CEO of the company. (Don’t let them take the paper home as they will find answers
on the Internet.)
Santa Fe Balloon Company offers balloon rides to tourists on a daily basis. The balloon rides
typically begin early in the day (6am). When the company hires a new advertising agent, he
recommends changing the ride time to 1:00 pm to attract more customers. You will act as a
science adviser and use your knowledge of heat transfer to write a letter explaining whether or
not the ride time should be changed. Be sure to explain your reasoning.
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Name
THE BOTTLE EXPERIMENT
Wear googles during the
experiment!
Beware of burns! Don’t handle or
touch hot or flaming objects.
Materials: per group: empty water bottle, cup of sand, balloon, ice, hot water, bowl wider
than the bottle, goggles. Conduct the experiment in groups of 3-4.
Procedure:
1. Remove the lid and pour about 2 inches of sand into the bottle.
2. Flatten the balloon and fit it over the mouth of the water bottle.
3. Draw a model of the set-up in the space below, adding any
labels that you can.
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Investigate:
Bottle Experiment
1. Pour hot water into a shallow bowl. CAREFUL!!
2. Place the bottle in the bowl and observe carefully.
3. In the space below, draw a model to explain what you observe. Add any labels
necessary.
4. In the space on the right, write a claim about what happened and provide
supporting evidence.
Model
Claim/Evidence
Discuss: Share your explanation and model with a partner. After discussion, revise
your model with any additional useful information.
Predict: Explain what you think would happen (and why) if the bottle was now placed in
a bowl of ice water. _____________________________________________________
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Investigate: Place the bottle in a bowl of ice to find out if your prediction is correct.
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THE TEA BAG EXPERIMENT
Wear googles during the
experiment!
Beware of burns! Don’t handle or
touch hot or flaming objects.
Materials: tea bag, heat proof surface such as a pottery plate or foil pan, match or lighter,
googles.
Procedure Set-Up
1. Remove the staple, string, and label from the bag of
tea.
2. If your bag of tea is not open on the ends, cut both
ends off and empty the tea leaves into a trash
container.
3. Unfold the bag of tea so that it is completely straight.
4. Use your fingers to open up the bag of tea.
You should have a shape resembling a cylinder.
5. Stand the cylinder on one end on a flat,
nonflammable surface. A dinner plate will work.
Predict: Make a prediction about what will happen when you set fire to the top of the
tea bag.
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INVESTIGATE:
Tea Bag Experiment
1. Using a lighter or match CAREFULLY ignite the top of the tea bag cylinder.
2. Observe CLOSELY. (You may repeat the investigation once more if needed.)
On Your Own:
Explain: Write a claim about what happened and provide supporting evidence.
Draw a model that shows what happened. Add necessary labels.
Claim and Evidence:
Model:
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Talk to Your Partner: Discuss your claim and related evidence with your partner.
Explain how your model shows what happened. Add any new information provided by
your partner in the space below.
Come to Consensus: Negotiate with your partner and develop the strongest claim
supported by the evidence.
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Heating and Cooling in the Real World
Read the information below. Highlight any new or confusing vocabulary.
Land and Sea Breezes
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Many of those who live and work along the shore know that water plays a role in how
winds develop along the coastline. Water has more capacity to absorb heat than any
solid or liquid except liquid ammonia. Water’s unique ability to store heat, but
without a large change in its own temperature, accounts for why land is warmer than
nearby bodies of water during the summer. This affects large inland lakes as well as
coastal regions.
During the day, air over the land is heated, becomes less dense, and expands upward,
pulling cooler air toward the shore from the surface of the surrounding sea water.
These cooling sea breezes can penetrate inland for considerable distances (25 miles)
even though they extend only a few hundred feet above the ground. The same
condition on inland lakes may penetrate for just a few miles.
At night, radiation cooling may cause the air over the land to become cooler than air
over the water, so air-flows in the opposite direction — a land breeze — occurs.
Without the sun, night-time differences between land and water temperature are not
as dramatic, therefore the land breeze is typically not as strong as a sea breeze.
In one east coast city, Newport, Rhode Island, the thermal conditions are so
predictable that you can almost set your watch by them. The southwest sea
breeze comes in around noon and produces fair-weather cumulus clouds.
Regardless of the overall weather pattern or wind direction, the sea-breeze
effect is so dominant that it blows until the land cools around sunset. And all
this is because of the uneven heating of land and water, or more specifically
because water has a heat capacity of two or three times that of land.
Read the text a second time. Underline information that explains how land and sea
breezes form.
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Use information from the text to make a model of a sea breeze on the picture below.
Add any labels that help explain the causes.
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Teacher Information: Explorations
Bottle Experiment Goals: Students should conduct the bottle investigation and discuss with a
partner. They should refine their models afterward. Facilitate and ask:
 Your bottle in the original drawing is empty. Is it actually empty?
 How could you show what is inside? For example, map makers use symbols to
indicate features, such as parks or lakes. Is there a way for you to do something
similar to show what is in the bottle?
 How does your model show what is happening. Do the labels you added show HOW it
happened?
(The students should eventually draw particulate models that show air in the original bottle, and
air molecules spread farther apart in the heated bottle and the inflated balloon.)
Explanatory Model: Ask students to create an
explanatory model (diagram) on chart paper to
show why the balloon inflates. Note that air
particle motion is indicated with arrows,
molecules are farther apart after being heated.
Tea Bag Investigation Goals:
The investigation can be conducted as an
elaboration to determine if students can apply
what they learned to the new situation.
As the tea bag burns, the air inside is heated, the
particles move rapidly, expand, and the air is less
dense and begins to rise. Cooler air on the
outside and warmer air on the inside creates a
thermal convection current. The ‘rocket’ effect
occurs because the ash left after burning is so
lightweight that the warm rising airs causes ‘lift
off’.
The OTC strategy is followed by groups of
students following the investigation. They should engage in argument to decide on the best
explanation of what happened. You may want them to create another chart for display.
Explanation Discussion: As students describe their understanding add the word
“convection” to describe a circulation create when heated air rises and cooler air falls.
ADDITIONAL INFORMATION
There is also a real world connection with this experiment. While vehicles like NASA rockets or
harrier jets (these are really amazing, look them up) use propulsion to achieve a vertical "liftoff,"
hot air balloons use a similar method to your rocket that you created with a bag of tea. Hot air
balloons use a burner to heat the inside of the balloon, creating the same air density change
that you made with your rocket. However, there is no mass change like when your paper turned
to ash. Instead, the air inside the balloon is heated much hotter than the air outside, creating an
envelope of air much less dense than the air outside. As a result, the balloon lifts off the ground.
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Land and Sea Breezes: Close Reading
To apply their new understanding to the real world students will do a close reading of Land and
Sea Breezes.
1. Tell students to read “Land and Sea Breezes” and identify unknown vocabulary.
2. Place them in groups of 3-4 and let them discuss their understanding.
Second Reading: Ask them to read the article a second time, underlining information that
explains how land and sea breezes form.
Students use the information to make a model of a sea breeze (You may want half the students
to make a land breeze as comparison). They should include circulation patterns and arrows as
well as labels. Facilitate and ask questions to encourage them to add more information.
a. Is there a way to use symbols to show how the air is moving? (arrows)
b. Can you use some of the new terminology from the article to label what is
happening to the air? (density, cumulus clouds)
Third Reading: Questions: Write two questions on the board and ask students to cite
specific information from the text providing quotes or paragraph numbers. (Write the
questions on the board, students can respond in notebooks or on Exit Slips.)
1. How do the bottle and tea bag experiment relate to the formation of land and sea
breezes? Cite evidence from the text and connect it to your observations.
2. Are heat and temperature the same thing? Provide evidence from the article “Land
and Sea Breezes” to support your answer.
(Sample response: 1: In paragraph 2 it states that when air over the land is heated during the
day it becomes less dense, it expands and rises. The same thing happened in the bottle, as air
was heated it became less dense and expanded blowing up the balloon, the evidence was the
balloon expanding. 2: Heat is not the same as temperature. In the article (para. 1) it says that
water can store heat without a large change in temperature so even though something has a lot
of heat present the temperature may not indicate that it does.)
Explain:
Students can share their land and sea breeze models and discuss what they have learned.
They should also indicate what areas of the article explain how to do the model.
Evaluation:
Students can write a letter to the Santa Fe Balloon Co. (page 1 of lesson) to explain why the
balloon rides should occur in the early morning. You may want them to complete the ‘Colorful
Water Extension” before they do the evaluation.
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Teacher Information:
Extension: Exploration: The Colorful Water Experiment
Post an essential question: Tell students they have learned about convection in gases and now
they will answer the essential question with additional investigations and reading.
EQ: “Does convection occur in all states of matter; solids, liquids and gases?”
This experiment is designed to help answer the essential question: Tell students that a final
evaluation will be to describe evidence and create an argument on their position related to the
question. They have information on gases from previous experiments and close reading. The
close reading on Convection will add an understanding of convection in liquids and solids.
Part 2 Inquiry: Students design their own experiment after being given ice, bags, and
additional hot water. During a class discussion they can share what they did and what they
have learned. Tip: If students decide to place baggies of ice and hot water in the tank, they may
need metal clips to secure the baggies to the edges, but let them decide on what method to use
in testing.
Teacher Instructions: Colorful Water Experiment
Tips: Clear plastic shoe boxes can be used for this experiment and small Styrofoam cups will
support the box and can also hold the hot water (it should not be boiling). You can heat the
water in a microwave and place in a foam chest until needed or use a hot plate.
Explain:
Explanatory Models: After students complete the experiment, ask them to draw a model
(diagram) to explain how the motion in the water occurred. They can add arrows and terms.
Question them if they do not show how the temperature variation may contribute to the
motion of the colors. Ask if they can add information to explain why this is happening. Ask
them if anything is happening that they can’t really see, but they know is occurring, or how they
could show the particles of the materials.
CHART: Explanatory Models: Provide each group with chart paper and ask them to outline their
experiment and provide a new explanatory model to show what is happening. Ask if they notice
any relationships to the first model, or if they want to refine any information. (optional)
Close Reading: After completion of model Session.
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After students have completed all the experiments and refined their models, ask them
to do the close reading at the end of this lesson.
Provide any annotations you want them to use. For example; highlight new vocabulary,
under information that helps answer the essential question. Etc.
They should also answer the two questions at the end of the article
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Evaluation:
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Argument Poster Presentation: Students should create an Argument Poster with the
essential question at the top. Underneath they outline their claim, and then list
evidence from experiments and text, they can also explain their reasoning on how the
evidence connects to the claim when they present to the class.
Model Display: Ask them to display models and explain what they learned to the class.
Encourage others to ask questions about the models.
Evaluate the quality answers to questions and completeness of individual lab sheets.
What’s Going On? Colorful Water Explanation- During the experiment, the cup of hot
water will heat water in the tub and cause the molecules of water and food coloring to begin to
move and spread. Students should be able to see a current forming. When the warm liquid
rises it cools at the surface and drops down toward the bottom, forming convection current.
They will see a more graphic model of this in the text.
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The Colorful Water Experiment
Wear Mitts and Goggles.
Wear Mitts and Use Caution
when handling containers of
hot water.
Materials: large plastic container of water, food coloring, pipette, 5 foam cups, hot
water, ice, 2 zipper bags for each group.
Investigation Set-Up: (Read through to make sure you understand what to do.)
1. Fill tub or container about 2/3
full of water.
2. Carefully balance the container
of water on 4 plastic cups (one
at each corner).
3. Add hot water to another cup
and carefully slide it under the
large container to a spot in the
middle. See diagram.
4. Squeeze 3-4 drops of food coloring into a pipette. Keep coloring at the tip.
5. Lower the pipette straight down into the water to the bottom, near the center.
6. Squeeze out a blob of coloring. DO NOT release the pipette after squeezing:
instead raise it slowly out of the water.
7. Observe carefully and make diagrams on the back at several intervals (2-3
min.).
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On Your Own:
Colorful Water
Explain: In the space below describe your observations and write a claim about what is
happening. Include supporting evidence.
Observations/Claim and Evidence
Model
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Talk to Your Partner: Discuss your explanation and add any new information your
partner provides in the space below. Add any questions you still have.
Questions you still have:
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Colorful Water: Revised Explanatory Model
Come to Consensus: Negotiate with your partner and develop the strongest claim
(supported by evidence) that explains what you observed.
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Inquiry Extension: The Colorful Water Experiment
Materials: In addition to the materials you already have; the tank of water, food coloring,
pipette, and foam cups you can use: plastic zipper bags, hot water, and ice.
Group Inquiry:
 Discuss with your group how you will conduct another related inquiry investigation.
 Explain your ideas in the space below.
 Conduct the investigation and write a conclusion. Follow Safety Procedures!
 Each Group Member! Draw a model (diagram) to explain what you have learned. Label
all parts. Compare with other members of your group and discuss.
Investigative Question:
Prediction:
Procedures:
Conclusions:
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Model: Draw a model (diagram) that shows what happened during the
investigation and explains why it happened. Be sure to label ideas and add any
terms you know.
Explanatory Model Diagram
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Close Reading
Student Information:
Types of Heat Transfer
The movement of energy from a warmer object to a cooler object is called heat transfer. Heat
is always transferred from a warmer substance to a cooler substance. There are three types of
heat transfer: radiation, conduction, and convection.
The transfer of energy through empty
space is called radiation. Heat transfer
by radiation takes place with no direct
contact between a heat source and an
object. For example, radiation enables
sunlight to warm the earth's surface.
You have probably experienced radiant
heating sitting by a campfire and
feeling the warmth or when you roast a
marshmallow by holding it close to the
flame.
Heat transfer within a material or between materials that are touching is called conduction.
In conduction the heated particles of a substance transfer heat to other particles through direct
contact. Examples of conduction might include burning your feet when walking on hot sand at
the beach, when a spoon heats up in a hot pot of soup or when you press the wrinkles out of
your clothes with a hot iron.
The transfer of heat by the movement of
currents or flow of material is called convection.
During convection, heated particles of a fluid
begin to flow, transferring heat energy from one
area of the fluid to another. Heat transfer by
convection is caused by differences in
temperature and density within a substance.
Density is a measure of how much mass there is
in a volume of a substance. When a fluid is
heated, the particles move faster. As they move
faster, they spread apart. Because the particles
of the heated fluid have spread out and are farther apart, they occupy more space. The fluid's
density decreases. But when a fluid cools, the particles move closer together and density
increases. (The exception would be when water freezes into ice and expands due to the
crystalline nature of ice.)
An example of convection can be seen when heating a pot of water on a stove. As water at
the bottom of the pot gets hot, it expands and becomes less dense. The warm, less dense water
moves upward, floating over cooler, denser water. At the surface, the warm water spreads out
and begins to cool. It becomes denser and gravity then pulls it to the bottom of the pan. Here it
is heated again and begins to rise. If you watch a boiling pot you may even see these currents.
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The flow that transfers heat within a fluid is called convection current. Heating and cooling of
the fluid and subsequent changes in the fluid's density, plus the force of gravity combine to set
convection currents in motion. Convection currents continue as long as heat is added to the
system. Convection currents occur in the water of the oceans and also affect weather patterns
in the atmosphere of the earth. For instance, on a hot sunny day, the surface of the earth is
heated by the sun’s radiant energy, conduction then heats the air above the earth. Convection
causes this heated air to rise and the colder air to sink. The rapidly rising air may cause huge
cumulonimbus clouds to form, resulting in sudden thunder storms we see during the summer.
Convection flow also occurs in the mantle deep in the earth. Geologists describe the mantle
as hot, solid rock, but believe it flows slowly. Heat from the core and the mantle itself causes
convection currents to form in the mantle. Hot columns of mantle material rise slowly, spread
out and push the cooler material out of the way. This cooler material sinks back into the
mantle. Convection currents like these have been moving inside Earth for most of Earth's
history. They are believed to cause the motion of the crustal plates described as Plate
Tectonics, which in turn produces earthquakes and volcanism.
Below: Comparison of convection in a boiling pot to the motions in the mantle.
TDQ: (answer on note paper)
1. According to the article, what evidence supports convection occurring in
fluids or gases? In solids?
2. In paragraph 4, what information could help you revise the models you
made of the experiments so that they provide clearer explanations of your
observations?
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Teacher Experiments and Demos: Transfer of heat energy by convection
Gases
Cut a coil out of card and suspend it by a thread
above a light bulb. The heat energy expands the air
lowering its density; this lower density air rises
causing the coil to rotate. This is simple but effective
demonstration of convection in a gas.
A circle of card about 5 cm across cut into a spiral
works well if the arms are about 1.5 cm. wide
leaving a disc in the middle to attach to the thread.
You might also try a foil coil with a candle inside.
Use a tall metal tube to show the
convection currents in a chimney (a piece
of metal pipe 1.5 m x 10 cm in diameter
works well). If a Bunsen is placed at the
bottom of the chimney and small pieces of
paper are introduced into the flame they
will be shot out of the top of the chimney
by the rising air currents!
Place a long open glass tube over a lighted
candle; it goes out due to lack of oxygen.
Repeat, but suspend a metal plate down the
center of the tube so that it hangs over the candle
flame. The flame stays alight because hot gases
escape up one side of the plate and fresh air is
drawn down the other bringing oxygen with it.
You may also raise the tube bottom off the table.
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Liquids
Get a shallow large diameter dish with a flat
bottom. (Plastic shoe boxes work well).
Support the dish on four Styrofoam cups.
Using a dropper, slowly release a small
amount of food coloring at the bottom of the
dish of water. Slowly remove the dropper,
taking care not to stir the water.
Observe what happens.
Put a cup of very hot water under the dish in
the middle of the dish. Observe the movement
of the color.
Repeat the experiment; but secure a zipper
bag of ice at one end of the dish and a bag of
hot water at the other. Observe.
Convection currents in a liquid can be easily seen
using a rectangular test tube. The test tube is filled
with water, the bottom right hand corner is heated,
and a few drops of food colouring are dropped in the
opening at the top.
The colour can be seen following the convection
current pattern.
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