When teaching convection cells, fronts, and sea/land breezes, I've explained how warm air rises and cool
air sinks. We've simulated this by spreading out, fanning ourselves, and standing on chairs as we get
hot, then bundling close together on the floor as we get cold. The kids have a good understanding of
this concept.
Now that I started teaching climate and explaining that it gets colder as you increase in altitude, some of
the kids are confused. I don't really know how to explain it either.
Do you have a kid-friendly explanation why temperature decreases as you go higher in altitude, even
though warm air rises and cool air sinks?
Thanks!
Bonnie Robinson, M.Ed.
5th Grade Teacher
Billingsville Elementary School
__________________________________________________________________________________________
From: elementary-request@list.nsta.org [mailto:elementary-request@list.nsta.org]
On Behalf Of Wayne A. Fisher
Sent: Sunday, November 25, 2012 12:50 PM
To: elementary@list.nsta.org
Cc: Robinson, Bonnie K.
Subject: FW: Warm Air Rises?
I am the Elementary Science Specialist for a large school district in NC ( 102 elementary schools).
I often receive emails from teachers asking for ideas/activities to help their students gain a better
understanding of science concepts.
Here is my reply to Ms Robinson's request for a "kid-friendly" explanation of why temperature decreases
with altitude.
I would be interested in any other advice I can share to help her enrich and enhance her science lessons.
Thanks!
Wayne Fisher, MS, MEd, NBCT
__________________________________________________________________
Hi Bonnie,
What a wonderful question! I like how you are helping your students grasp science concepts by using
hands-on/kinesthetic activities. When students can add motion and model science concepts, they gain a
deeper understanding of the fundamentals of science.
The short answer to your question is this .... it's the fact that as you go higher in the atmosphere the
pressure decreases, causing the rising air to spread out (expand) and thus the temperature decreases.
Here's a longer answer and one that you can use to decide how to help your 5th grade students wrestle
with the science concepts involving temperature, pressure, water cycle, states of matter, etc.
Ask your students what happens to the temperature of a warm body of air ( air mass) as it spreads out.
For example, you have a warm mass of air that is rising and it is forced ... somehow ... to spread out
into a larger area.
The three choices your students can tell you are 1) the air gets hotter, 2) the air gets cooler, or the 3)
the temperature remains the same. Have your students pair/share and talk for a minute about their
prediction and write it down.
Rather than tell the students the answer, let them discover the answer for themselves using "hands-on"
science! Ask them to place the palm of their hand in front of their mouth, take a deep breath, and
exhale with their mouths wide open, similar to what you would do if were trying to fog a mirror or see
their breath on a cold day. Ask them what is the temperature of the air; the answer should be warm,
hot, or words to that effect.
Then ask them to repeat the procedure, but in this case, blow as if you were blowing out a candle. What
do they observe about the temperature of the air now? The answer should be cool, cold, or words to
that effect. What can we conclude about the temperature of a hot air mass when it is forced upwards
and then allow to spread out? Answer -- the temperature of the air decreases. Why?
As you go higher into the atmosphere, is there more or less air pressure? Answer - less air pressure.
Why? Air pressure is the weight of the air pushing on a surface. Is there more or less air the higher you
go above the earth? The answer is less air --- the atmosphere "thins out" as altitude increases; at what
height does the atmosphere stop and space begins?
If there is less air as you go higher above the
earth, is there less air pressure? Yes! Less air pressure means rising air will spread out the higher it
goes above the earth. What have we learned about the temperature of air as it spreads out, or
expands? The temperature goes down!
To extend this concept of hot air cooling as it rises, what do we know about the behavior of air as it
cools? From what your students have already investigated, they should be able to conclude the particles
of air that are cooler tend to slow down (move less quickly) and eventually reach a point where the water
particles in the air will condense and form clouds leading to a mini-lesson about the water cycle. A good
example of hot air rising and spreading out as it cools is the exhaust from smokestacks or power plants;
in southwest Charlotte this natural display is often seen from hot air rising from the nuclear power plant
near Lake Wylie.
A more detailed explanation of why temperature decreases with altitude would involve peeling back the
layers of our fundamental understanding of what temperature is. In high school or beyond, students
learn that temperature is the average kinetic energy of the particles in a system. How fast those particles
move will determine the temperature of the object. Note, heat energy is different than temperature, but
that's another whole discussion. An excellent series of books from NSTA that helps us better understand
science concepts is the "Stop Faking It" series.
For 5th graders, the big idea about temperature is that it measures how hot or cold an object is and is
related to the motion of the particles that make up the object being measured. You have already
explored the relationship between temperature and motion with your previous lessons. Keep up the
good work exciting your students about science!
Wayne
Great question!
Here is a possible model that may help understand the effects of pressure changes. Stack about 6 donut
magnets on a pencil or a dowel rod so that they are all repelling. Have kids look at the spacing between
the magnets and they will notice that the magnets at the bottom of the rod are closer together than the
top ones. Working in teams have students explain what causes the difference in spacing. What
happens to the spacing between the bottom two magnets if we remove one magnet from the top of the
pile? Etc. Help connect the observations to the idea of weight. Or maybe you could have kids stack 4
or 5 text books on top their hand one book at a time (a really good use for textbooks). How does the
pressure on their hand from increasing weight change? You could also but some soft foam rubber or a
sponge on a table and then alternately stack books and foam and you may be able to visualize the same
idea as with the magnets (I have not tried this). This would not help explain why warmer air rises, for
that we need to go to sink and float for another model.
So, as you describe, in the real life of the kids warm air usually rises and gets cooler within the
troposphere etc., but in the larger context of the total atmospheric layers on Earth, that the kids
probably cannot really visualize, there are other factors that come in. Above the troposphere the
pattern of getting colder us you go up does not necessarily continue. But going there and understanding
what is going on is not appropriate for grade 5.
Bill Schmitt, The Science Center of Inquiry
I use a water model of warm (red food color) and cold (blue food color) poured into a basin of room
temp water from either end. This vividly demonstrates the greater density of the cold matter. My
students understand that air is heated by radiation from the earth. The higher in altitude the heated air
rises the further it is from the source of additional heating and therefore cools. Matter moving away from
a source of radiative heating will cease to warm at the same rate. This could be demonstrated with a
light and a thermometer or LabQuest.
Ruth Kiser
Fifth Grade Teacher
Mountain View Elementary, Catawba County Schools
How about this analogy:
Close to the surface of the earth the molecules of air are closer together than when we go to higher
altitudes. Molecules of air transfer heat when they contact you. So let’s think of them as hot potatoes.
When a hot potato touches you, you can feel the heat. At lower latitudes the potatoes are closer
together so you get hit by them more often than when you go to higher latitudes. More hits means
more heat transfer. If the potatoes are further apart, like at higher altitudes, then you will get hit less
often and, even if the potatoes are a bit hotter, you don’t get as much heat transfer.
Now, you can take the potato analogy further and build in the particle structure of solids, liquids and
gasses and heat capacity of the different states of matter. You can feel the heat of the air when you put
your hand into an oven momentarily. But, when you touch a pan (which is at the same temperature as
the air in the oven) you get a quick and intense burn. This is because the ‘hot potatoes’ in solids are so
closely packed that your hand touches many more of them than when you just put your hand in the
widely spread out ‘hot potatoes’ in the air in the oven. Touching more potatoes means more heat
transfer.
Hope this helps,
Gabe Kraljevic
Science Curriculum Consultant, K-12
Manitoba Education
Thanks Gabe!
I like the hot potato analogy!
That’s something 5th graders can understand, plus heat transfer is also a concept that is new to our 5th
grade curriculum and teachers are asking for help with that concept.
One thing I need to think about is how heat energy is being transferred. With air movement, it is more
convection rather than conduction that allows heat energy to flow from the hotter body (usually the
person’s skin) to the colder body ( the body of air).
For the oven example, the temperature of the air is greater than body temperature so the air feels hot
as the hot potatoes transfer heat energy to one’s hands.
I am thinking that if we use heat exchange, rather than heat transfer, it may avoid the confusion about
the direction heat energy is flowing.
Also, with the over example, some of the heat exchange is due to convection, but most of the heat
energy being generated is radiation, which is another difficult concept to explain.
I think I need to read my Stop Faking It book on energy again! It’s a new book in that series and I
attended a workshop by the book’s author at an NSTA Conference in Atlanta, Georgia.
Wayne