January 2008, Tips and Techniques for Creative Teaching
Convection in a
F i s h Ta n k
As a high school science teacher with
limited funds, I am always looking
for demonstrations that are both costeffective and visually stimulating.
This demonstration is more captivating than a lava lamp and is a great
method of modeling convection using
materials most science teachers already
have at home or in the classroom.
Understanding convection is fundamental for students to fully grasp
the science behind large-scale events
on Earth, such as global wind patterns, plate tectonic movement, ocean
current patterns, and hydrothermal
vent dynamics. Convection can also
help students understand how car
engines are cooled, how radiators
heat a room, how a pot of water boils,
and how lava lamp fluid moves up
and down. Using a convection demonstration in a classroom emphasizes
the importance of convection while
captivating students’ interest.
Materials and directions
The following materials are needed
for you to lead the convection demonstration:
u one 10 gal (38 L) fish tank
u two dictionaries or two stacks
of magazines, 5–7 cm high
u 100 pennies
u three tea light candles
u bottle of red food coloring
u bottle of blue food coloring
u water
u matches
Place the two dictionaries 20–25
cm apart on a flat surface and set the
fish tank on the dictionaries (Figure
1a). Make sure that the tank is stable,
level, and not hanging off the sides
62
The Science Teacher
of the books. Place the 100 pennies
in rows across the center of the tank.
Make the first layer three rows wide,
then stack two additional rows of
pennies on top of the first layer of
coins. The second and third layers of
pennies should be stacked to overlap
the gaps between the bottom pennies
(Figure 1b). This creates a groove
between the pennies in the top two
rows that will help hold the food coloring in place.
Fill the tank with water to about
5 cm from the rim of the tank. Place
the candles in a line below the fish
tank directly under the pennies.
Take the bottle of red food coloring
in hand and, with minimal disruption to the water, move your hand
to the bottom of the tank and slowly
squeeze the red food coloring into the
groove made by the pennies. (If done
correctly, the food coloring will stay
resting on the pennies, see Figure 1c.)
Stop squeezing the bottle and slowly
remove your hand and the bottle
from the fish tank, trying to disturb
the water as little as possible. After
the water settles, light the candles under the fish tank. The demonstration
is ready to begin (Figure 1d).
Within one minute after being lit,
the candles will heat the pennies and
start the process of convection. The
hot pennies heat the water and the expanded, less dense water begins to rise
away from the heat source. The red
food coloring colors the heated water,
allowing students to see the water
rise. The red color represents the hot,
less dense water rising (Figure 1e). As the heated water and red food
coloring rise away from the pennies,
the red-colored liquid is still hot, but
it begins to cool as it moves away
from the pennies. The red-colored
liquid cools down and spreads out as
Figure 1a.
Figure 1b.
Figure 1c.
Figure 1d.
Figure 1e.
Call for Papers
The Science Teacher (TST), a peer-reviewed journal, is seeking manuscripts that describe new and
creative ideas for the secondary science classroom.
Manuscripts should provide worthwhile ideas
and practical help for teachers as they relate to the
themes listed below. TST also always encourages
manuscripts outside of the listed themes for consideration by our peer-review panel and field editor.
Physical Science
General Topics
SubmiSSion DeaDline: ongoing
SubmiSSion DeaDline: ongoing
Understanding the relationships among the
properties, changes, and structure of matter is a
central theme in the high school science curriculum. Concepts of motion, forces, and energy are
important in all the sciences, helping students
understand everything from the transport of
materials across cell membranes to the movement of planets and galaxies. TST is interested
in manuscripts that describe classroom activities involving new and creative ideas in physical science.
Do you have an article idea in mind that does
not fit with one of TST’s themes? Write about
it and submit it for review! General articles, not
targeted to a requested theme, are published in
every issue. If you have written a manuscript
on a secondary education topic, please submit it
at any time.
The Fine Print.
Manuscripts should describe successful lessons
implemented in secondary classrooms, as well
as provide specific details for educators who
might wish to use the activities with their
own students. The manuscripts should include
appropriate assessment tools and specifically
reference the National Science Education
Standards where appropriate. Examples of
student work to illustrate results of a successful
lesson are encouraged, as are figures, sidebars,
and accompanying photos. Author Guidelines
can be found on page 25 of this issue and online
at mmm$dijW$eh]%',/$
48
The Science Teacher
Idea Banks
SubmiSSion DeaDline: ongoing
TST is always seeking Idea Banks—short articles of about 1,000 words. During your summer
vacation, did an experience reignite your enthusiasm for science and teaching? Is your school
involved in a successful partnership with the local community? Do you have an original, howto lesson that you have developed? If you want
to share an experience, activity, or classroom tip,
but don’t think it will work as a feature-length
article, consider submitting an Idea Bank!
Commentaries
SubmiSSion DeaDline: ongoing
Commentaries of approximately 750 words on
any secondary education topic are accepted at
any time. Do you have thoughts on science education that you would like to share with your
peers? Write up a Commentary and submit it
to TST for review.
January 2008
63
Figure 1f.
Figure 1g.
Figure 1h.
Figure 1i.
it continues to move up, away from
the heat source (Figure 1f).
Place two drops of blue food
coloring in rapid succession 2–4 cm
from both sides of the rising red food
coloring (Figure 1g). The blue food
coloring represents the cooled, dense
water descending back to the depths
of the fish tank.
The dense blue liquid will be
pushed away from the center of the
tank by the laterally moving, cooling
red water at the upper portion of the
tank. Then, as the blue food coloring descends, it will be pulled back
toward the pennies to replace the
water that is rising up away from the
heat source (Figure 1h).
Once the blue-colored water
comes in contact with the hot pennies, it will rise back up with the redcolored water to begin the process all
over again (Figure 1i).
Thoughts about the
demonstration
Pre- and Postdemonstration questions.
Predemonstration
1. Why do hot air and hot water rise?
2.Why do cool air and cool water sink?
3.When air above a flame rises, what happens to the air beside the flame?
4.When air moves up and away from its heat source, does it remain the same
temperature?
5.Draw a diagram of the air movement that would happen around the head of a
candle. Use arrows to represent air flow and be sure to label the hot and cold
air.
Postdemonstration
1. Draw a diagram of the “Convection in a Fish Tank” demonstration. Use arrows
to represent water flow and be sure to label your hot and cold water.
2.How does the circulation of water in the fish tank differ from the air flow in
your earlier drawing?
3.What factors made the water move sideways in the demonstration?
4.What nonhuman influences make the air beside a candle move sideways?
5.Briefly describe three places in a house where convection might take place. 64
The Science Teacher
The demonstration of a convection
cell is complete once the blue-colored
water reaches the pennies. However, to demonstrate how convection
moves tectonic plates, a simple addition can illustrate divergence. Float
two plastic bottle caps 2–4 cm apart
on opposite sides of the uplifting
fluid. The bottle caps represent tectonic plates. The current will slowly
pull the caps farther apart from each
other showing how divergence takes
place.
I have developed and modified
this demonstration of convection
over the past four years. The most
noticeable advancement to the demonstration happened when I added
pennies to the model. The metal
pennies heat up faster than the glass
of the fish tank and pennies are
an inexpensive, readily available
resource. Without the pennies, the
convection process takes much lon-
2008 Area Conferences on
Science Education
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Share Your Good Ideas…
Submit a session proposal for NSTA’s 2008–2009 conferences.
www.nsta.org/conferences
ger and is much less dramatic. Once
the pennies are set into place, the
food coloring rests on and between
them, which helps keep the food
coloring from spilling out in a messy
puddle over the bottom of the fish
tank. In essence, the pennies have
streamlined this demonstration into
a practical classroom tool.
Classroom reaction
I have used this demonstration
in my 9th-grade Earth science
classes and my 11th- and 12th-grade
oceanography classes. In both settings, students appear captivated by
the colors and swirling fluid. They
ask numerous questions about how
the demonstration works and often
want to see what happens when
food coloring is added to other areas within the tank. I have even had
two students on separate occasions
come in the following day and tell
me that they had gone home and
performed the demonstration for
their families.
As part of the final exam in my
oceanography class, I have students
label and diagram a convection cell.
Many students actually draw a twodimensional version of this demonstration—the completeness of the
diagrams suggests that the demon-
stration had a lasting effect on these
students and enhanced their ability
to understand convection. Convection is a recurring concept in Earth
science, meteorology, and oceanography. Demonstrations such as this
one are an inexpensive, effective way
to make a typically invisible concept,
such as convection, become visible,
tangible, and exciting.
Chris Freeman ([email protected])
is an oceanography teacher
at Floyd E. Kellam High School
in Virginia Beach, Virginia.
International
P o l a r Ye a r i n t h e
Classroom
This past March the global science community kicked off the
International Polar Year (IPY) with
celebrations and ceremonies around
the world. IPY is one of the most
ambitious international science programs ever organized, currently involving over 60,000 scientists from
63 countries. The goal is to broaden
humankind’s understanding of the
Arctic and Antarctic, examining a
wide range of physical, biological,
and social science topics in order to
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The Science Teacher
more fully comprehend the critical influence polar regions have on
the rest of the planet. Research will
take place in multiple areas—exploring the land, people, oceans, ice,
atmosphere, and space—to create a
legacy of knowledge that can help
us better understand complex topics
such as global climate change and
life in extreme environments.
The IPY campaign also aims
to educate and excite the public
about polar science, helping to train
the next generation of engineers,
scientists, and leaders. There are
many exciting opportunities for
teachers and students to become
involved, gain access to cuttingedge research, and connect with
scientists as they conduct research.
The following is a list describing opportunities—supported by
the National Science Foundation
(NSF), National Aeronautics and
Space Administration (NASA), and
National Oceanic and Atmospheric
Administration (NOAA)—for
teachers to bring IPY into classrooms around the nation.
NSTA Conference
symposia and follow-up
web seminars
Many teachers participated in IPY
symposia at NSTA’s Regional Conferences over the past two years,
and those planning on attending
the National Conference in Boston this March should be sure to
register for one of the symposia
to be held there. The National
Conference symposia will feature
presentations from leading scientists and hands-on activities created by master teachers to support
the science presented. Online web
seminars will follow the symposia
to further professional development
once teachers return home. All the
information can be found on the