Convection Connection Project. University of Colorado at Boulder

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2 Convection Connection Project University of Colorado at Boulder Department of Physics Dr. Michael Dubson, Faculty (Featured Scientist and Activity Guide Scientific Advisor) Cooperative Institute for Research in Environmental Sciences Dr. Alex Weaver, Director, K-12 Outreach Program (Featured Scientist and Activity Guide Scientific Advisor) Program in Atmospheric and Oceanic Sciences Scott Kittelman, Faculty (Technical Support) Department of University Communications Bobbi Barrow, Executive Director Monteith Mitchell, Project Manager Wynn Martens, Community Affairs, Director Dirk Martin, Broadcast Services Coordinator Science Discovery Carol McLaren, Director (Project Advisor and Activity Guide Consulting Editor) Tara Chace, Special Projects Coordinator (Activity Guide Editor) Check out the Convection Connection website NEWS 4 Staff Marv Rockford, General Manager Angie Kucharski, News Director Larry Green, Colorado's Weatherman Jeff Gurney, Producer Logan Smith, Photographer Mike Porras, Photographer Tom Marès, Graphic Design (Illustrator/Designer: Activity Guide and Poster Producer) Vikki Olesen, Marketing Account Executive Check out the NEWS 4 website at 2

3 Convection Connection Day 1 - Overview Activity Guide Take a good look at the Convection Connection poster (pictured in black and white on the cover of this guide)! Hot air balloons and floating raisins, lava lamps and whales, palm trees and pots of boiling water - how in the world are all these things connected? You've got it: CONVECTION! Convection is found in the oceans, atmosphere and even the earth's mantle and sun. Convection explains many phenomena in the environment, and can be demonstrated in myriad fun experiments, some of which are included in this activity guide. So join us as we consider the density of fluids - air, water, and molten rock - and how density relates to convection; it should prove to be an exciting journey of learning! 3

4 Day 2 - Density Concepts: Density is mass divided by volume. More mass in a space makes for a more dense object. Imagine three cubes of the same size: one is granite, one is wood, and one is styrofoam. The granite has more mass, and is the most dense; the wood does not have as much mass, and is not as dense; and the styrofoam, with the least mass, is the least dense of the three cubes. Fluids also have different densities. Imagine a cup of plain water. If we dissolve one tablespoon of salt in the water, we still have the same volume -- one cup of fluid -- but the cup of fluid now has more mass, because there are more molecules (salt and water) packed into the cup than there were when we just had water in the cup. A cup of salt water is more dense than a cup of plain water. 4

5 Density Activity Purpose: To observe density of fluids and solids together Materials: Dark-colored pancake syrup Blue food coloring Water Vegetable oil 600 ml beaker or glass jar (with straight sides) Selection of objects to float (For example: corks, paper clips, grapes, marbles, small plastic piece, little stick, pebble, etc) Procedure: 1. Pour syrup into the container until it is about 1/4 full. 2. Slowly pour the same amount of vegetable oil into the container. 3. Put just enough food coloring in some water to make the water light blue. 4. Slowly pour the same amount of blue water into the container. 5. Observe how the liquids layer. 6. Now slowly add objects to see if they float or not, and if so on which liquids. Explanation: The liquids layer because they have different densities. A liquid that is more dense can hold up a liquid that is less dense. The oil is less dense than the syrup so it floats on top of the syrup. The water is also less dense than the syrup, but it is more dense than the oil, so the oil floats on top of the water which floats on top of the syrup. Solid objects have different densities as well. By observing where the solids float you can tell whether they are more or less dense than the various liquids, and each other. 5

6 Day 3 - Heat Concepts: A fluid is anything that can flow, such as a liquid (water), a gas (air), and molten rock. All fluids are made up of free flowing molecules. As the temperature of a fluid increases, molecules move faster, bouncing off each other more vigorously, and thus moving further apart from one another. As more space is created between the molecules -- there are fewer molecules in a given volume -- the fluid becomes less dense. Likewise, as the temperature of the fluid decreases, molecules move more slowly, and become closer to one another. When there is less space between the molecules -there are more molecules in a given volume -- the fluid becomes more dense. Heat Activity #1 Purpose: To see how temperature affects the speed of molecules Materials: Two small clear glass jars (baby food jars work well) Red and blue food coloring (can use any two colors) Two eye droppers Paper and pencil Hot water Cold water Procedure: 1. Fill one glass half full with very cold water, and one half full with very hot (not boiling) 2. Draw about 4 drops of blue food coloring into one eyedropper, and 4 drops of red food coloring into the other eyedropper. Try to have the same amount in each. 3. Hold the blue dropper over the cold water, and the red over the hot water near the surface of the water, but not touching it, and squeeze to empty the droppers at exactly the same time. 4. Compare how the food coloring moves in each container. Did the color spread more rapidly in one glass than the other? If so, what was the temperature in that glass in relation to the other glass? 6

7 Heat Activity #2 Purpose: To observe how temperature affects density Materials: 4 small, clear, identical glass jars (baby food jars work well) Hot water (not quite boiling) Cold water Red food coloring Blue food coloring Stir stick 2 thin stiff clear plastic squares that will cover the opening of the jars Shallow baking pans or pie pans to catch spills Procedure: 1. Place the four jars in the shallow pan. Fill two with hot water, and fill two with cold water. Fill the jars to the brim - the very top! 2. Place a drop or two of red food coloring in the two jars with hot water. Stir. Place a drop or two of blue food coloring in the two jars with cold water. Stir. 3. Place one plastic square on a hot water jar, and flip it over (carefully holding the middle of the plastic). Place it on top of a cold water jar. Place one plastic square on a cold water jar, and flip it over (carefully holding the middle of the plastic). Place it on top of a hot water jar. You should now have a hot jar on top of a cold jar, and a cold jar on top of a hot jar. 4. Now for the tricky part! Carefully line up the edges of one set of jars, and applying a bit of pressure to the top jar, slide the plastic out from between the two jars. Do the same to the other set of jars. 5. What happens in each pair of jars? Explanation: When the cold water is in the top jar, the cold water sinks down, displacing the hot water. This happens because the cold water is more dense than the hot water, causing the cold water to flow to the bottom of the liquid column, while the hot water flows to the top. When the hot water is in the top jar, the hot water remains on top of the cold water. This happens because the hot water is less dense than the cold water, allowing it to remain at the top of the column of liquid. 7

8 Day 4 - Air Pressure Concepts: Air exerts pressure on whatever it touches. The Earth is surrounded by an atmosphere which is about 80 miles thick. All this air produces a pressure of about 14.7 pounds per square inch at sea level. This pressure is called atmospheric pressure, and everything on Earth experiences this pressure - including you! An empty can does not collapse, because there is air inside as well as outside of the can. But if the air inside the can is removed, there is no pressure inside, and the outside air pressure will cause the can to collapse. Air pressure changes with temperature. If the volume of air is kept constant, and the temperature is increased, the speed of the air molecules increases, as does the pressure. If the temperature is decreased, the air pressure also decreases. Air Pressure Activity Purpose: To see the effects of air pressure Materials: 2 Empty aluminum soda cans Water Hot plate Pan with about 1 1/2" of cold water Safety goggles Tongs Procedure: Trial #1 1. Put on safety goggles. 2. Put about 1/2 inch of water into one can and place it on the hot plate. 3. The moment a wisp of steam is visible coming out of the top of the can, remove the soda can with tongs, and quickly turn it upside down in the pan with cold water. 4. What do you observe? Trial #2 1. Keep your safety goggles on. 2. Put about 1/2 inch of water into the other can and place it on the hot plate. 3. When the water is boiling well (steam will be coming out of the top of the can), remove the soda can with tongs, and quickly turn it upside down in the pan with cold water. BE VERY CAREFUL TO KEEP HANDS AND FACE AWAY FROM THE STEAM! 4. What do you observe? 8

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10 Day 5 - Buoyancy Concepts: Whether something sinks or floats depends on its density relative to the density of the surrounding medium. The ability to float is called buoyancy, and there are different degrees of buoyancy. For example: a solid block of granite sinks in water because granite is more dense than water - it is not buoyant in water; a helium balloon floats on air because the balloon containing helium is less dense than the air below - it is buoyant in air. Buoyancy Activity Purpose: To observe the buoyancy of raisins, and how their buoyancy can change. Materials: 600 ml beaker or other large glass jar About 25 raisins (2 oz. Box) 2 cups of water 1/4 cup vinegar 1 teaspoon baking soda Procedure: 1. Put the raisins into a container of water and remove any that float. Put those back in the box. 2. Pour out the water, and set the raisins that didn't float aside for the next steps. 3. Put 2 cups of water and 1/4 cup of vinegar in the large jar 4. Add 5 to 10 raisins to the jar. 5. Add one teaspoon of baking soda to the jar. 6. Observe the raisins. Explanation: The raisins sink because the force of gravity pulling them down is greater than the upward buoyant force exerted by the liquid. The gas bubbles act like tiny balloons that make the raisins light enough to float to the surface. At the surface the gas bubbles are knocked off, and the raisins sink to the bottom until more bubbles attach. The bubbles change the raisins' buoyancy causing them to rise and sink. 10

11 Day 6 - Convection Concepts: Convection is the transfer of heat by the movement of a substance from one position to another. Convection can be forced, such as occurs in the heating systems of many houses, or natural, such as occurs in the transfer of heat in fluids - air, water and molten rock -- due to density differences. A hot air balloon is a wonderful place to "see" convection due to differences in the density of air. As the lowest layer of air in the balloon is heated, it becomes less dense and rises. As that layer nears the top of the balloon it has become cooler than the layer now being heated, and thus sinks, becomes heated and rises again. This process is called convection. The overall temperature of the air in the balloon increases, and eventually makes the balloon buoyant (less dense than the air around it), and it rises from the ground. 11

12 Convection Activity Purpose: To "see" convection by building and launching a hot air balloon. Materials: One 60 x 20 piece of stiff paper for pattern Tissue paper (16 sheets, 24" x 30", various colors except black) Cutting pattern Pins (about 6 per balloon) Scissors (2) Rubber cement or glue sticks (2) Fishing line for tether (50 foot roll) - optional Wire (24", 16 gauge, or use pipe cleaners) Wire cutters Dryer duct chimney apparatus (about 24") Propane stove Procedure: 1. Using the tissue balloon pattern instructions, draw and cut out a pattern and set it aside. Tissue Balloon Pattern Instructions: a. Fold a piece of paper (60" x 20") lengthwise. b. Measure and mark points as shown. c. Connect the dots. d. Cut out the pattern, so that the fold is in the middle. 2. Overlap two pieces of tissue paper to make one 5 foot long panel and use the glue stick or rubber cement to glue the 2 pieces together along the 24" edge. Repeat using 16 pieces of tissue paper. You will have a total of 8 long panels. Be creative with colors. Plan how your balloon will look. 3. Place the long panels in an even stack. Straighten them and smooth them out. 4. Fit the pattern made in step 1 over the sheets and pin it in place. Be careful not to tear the tissue paper. 5. Cut out the tissue paper along the pattern. Carefully remove the pins and the pattern and save them. Keep the tissue sheets in a stack. 6. Glue the tissue panels together to make the balloon: a. Take panel 1 off the stack, and lay it flat on a table. b. Lay panel 2 on top of panel 1, so that one side of the bottom panel extends 1" past the edge of the top panel. 12

13 c. Fold that 1" margin of the bottom sheet over the edge of the top sheet and glue it down. d. Lay panel 3 on top of panel 2, so that the unglued side of panel 2 extends 1" past the edge of panel 3. e. Fold that 1" margin of panel 2 over the edge of panel 3 and glue it down. f. Continue gluing the panels together on opposite edges. g. When all are glued together it will be in one long line, folded like a fan. h. Check that the panels are folded this way, but don't open it up yet. i. Glue the first and last panels together as you did the other panels along their unglued sides. Now you can open the balloon to see that you have a circle 7. Lay the balloon flat again. Cut a circle of tissue to cover the top opening and glue it over the top hole in the balloon. 8. To hold the bottom of the balloon open: Form the wire or the pipe cleaner into a circle the size of the bottom opening; gently open the bottom edge of the balloon and position the wire on the inside about one inch up from the edge; fold the tissue over the wire and glue in place. 9. Gently open the finished balloon and check for large holes, being careful not to make any new ones! Patch any holes with pieces of tissue paper cut to fit. Tiny holes are ok. 10. To launch the balloon, place the dryer duct on the propane stove to form a chimney. Have a couple of students, WITH A TEACHER, help to hold the balloon over the dryer duct. Turn on the stove and allow the balloon to fill with hot air. When the balloon begins to feel warm, and as if it can float, it is ready to be launched. Count down, give it a gentle push and WATCH IT FLY!! Important Safety Note: An adult should be in control of the stove and the hot dryer duct. Use hot pads if you must handle the dryer duct after it has been heated. Explanation: Again, it's all about convection! Convection occurs in the balloon as the warm air rises and the cooler air sinks. The balloon fills with air that is warmer than the air surrounding the balloon, and as it does so the balloon becomes less dense than the surrounding air. The balloon will stay afloat as long as the air in the balloon stays warmer (less dense) than the air around it. 13

14 Day 7 - Convection in the Atmosphere Concepts: We expect that convection occurs in the atmosphere because air is a fluid -- air molecules are free to move -- and because there are areas of warm air and areas of cool air. Clouds are visible proof of convection: hot moist air rises; eventually it cools down and condenses (water droplets form). The clouds we see are these tiny water droplets. A thunderstorm, also called a convective storm, is the most dramatic example of convection in the atmosphere. Thunderstorms build due to a variety of weather conditions. One example is when a body of warm air is forced to rise quickly by an approaching (sinking) cold front. A strong persistent updraft of warm, moist air is formed. The approaching cold front helps build the updraft into a cumulus cloud, which eventually builds into a cumulonimbus cloud up above 30,000 feet. Then a downdraft forms bringing cold air and precipitation from high in the cloud to the ground. 14

15 Convection in the Atmosphere Activity Purpose: To observe how changes in air temperature cause convection currents. Materials: Cardboard box about the size of a 10-gallon aquarium (Note: A 10-gallon aquarium can be used. If it is, then you just need a piece of card board that snugly fits on the top.) Two glass lamp chimneys (clear plastic bottles such as Gatorade bottles also work) Pencil Scissors or sharp knife for cutting cardboard Wide transparent tape (package tape works well) Transparent plastic wrap Matches Incense to produce smoke Tongs One cup of steaming hot water Procedure: 1. Cut off the flaps of the cardboard box top 2. Position the box so that the opening makes one "side" of the box, and the top is a long-side of cardboard. 3. In one short end of the box cut a door that can be opened and closed. 4. Position the chimney lamps about an inch from the two short edges of the box top. 5. Trace a snug circle on the cardboard around the bottom of each chimney lamp. 6. Cut out the circles and fit a chimney lamp into each. 7. Seal around the chimney lamps with transparent tape. 8. Use the plastic wrap to cover the front of the box; seal it well to the cardboard using the transparent tape. 9. With tongs, carefully put the cup of steaming hot water in the box under one lamp chimney. Shut the cardboard door. 10. Hold the smoking incense, with the smoking end right at the opening of the other lamp chimney. 11. What happens to the incense smoke? Please note: If the inside of the box is painted black, the smoke may be more visible. Be sure to stay very still while observing the smoke in the box; any drafts will interfere with the convective currents. 15

16 Explanation: This is called a convection box. When hot water is placed under a lamp chimney, it will heat air that will then rise. Thus, the air outside the box will be drawn down to replace the air that is rising out of the box. The smoke from the incense shows the convection current. 16

17 Day 8 - Convection in the Oceans Concepts: Oceans are never still; the Coriolis Effect, the gravitational pull of the moon, surface winds, variations in salinity and water temperature all play a part in the continuous motion of ocean water. There are areas of warm water and areas of cool water in the oceans, indicating that convection is taking place. The most dense water in the oceans is found at the poles, where cold, salty water sinks to the bottom of the sea; because the world is not still this water starts to flow towards equator. As it moves, surface currents (including the Gulf Stream) move warmer, fresher water in to take the place of the sinking more salty, cold water. This "global conveyor belt," takes about 1,000 years to complete one cycle. E. Greenland Labrador Norweigan Oyashio Alaska N. Atlantic Drift Kuroshio N. Pacific California Gulf Stream Canary N. Equatorial N. Equatorial N. Equatorial Somali S.W. Monsoon Equatorial Counter Equatorial Counter Agulhas S. Equatorial S. Equatorial S. Equatorial Brazil W. Austrialian E. Australian Peru Benguela West Wind Drift West Wind Drift West Wind Drift 17

18 Convection in the Ocean Activity #1 Purpose: To discover how salinity affects the density of water. Materials: Aluminum pie pan Small piece of clay Clear, colorless plastic straw (only clear will work well) Blue, green and red food coloring ml beakers, each filled with 500 ml of water Salt Eye droppers, one for each solution Paper towels for cleanup Density Currents Worksheet Blue, green, and red colored pencils Procedure: 1. Make the salt solutions: 2. "Ocean water:" 500 ml of water with 90 ml of salt. Stir until dissolved and then add 20 drops of blue food coloring. 3. "Brackish water:" 500 ml of water with 30 ml of salt. Stir until dissolved and then add 20 drops of red food coloring. 4. "Fresh water:" Just 500 ml of water. Add 20 drops of green food coloring. 5. Stick the plastic straw in a square cube of clay. Make sure the straw doesn't quite go through the bottom of the clay. Pour some tap water into the straw to make sure that it is leak proof. To empty the straw, pick up the whole assembly. 6. Explain to the students that the difference between the three solutions is just color and salinity. The students job is to figure out which is the fresh water, brackish water (found at the mouth of rivers), and ocean water. The students should hypothesize which type of water is the most dense, least dense, and in between, and why. 7. Using the worksheet provided, have the students document their trials until they have layered the three liquids successfully. To test the liquids, the students should drop about drops of the first color they plan to use slowly down the straw with an eye dropper - it works best to tip the straw slightly. Repeat the procedure with the second and third color. If the liquids mix, the students should start over with a new trial. If they layer perfectly on the first trial, have them try different orders to compare the difference. After each trial the straw should be emptied into the pie pan. 18

19 1. Hypothesize which type of water (ocean, fresh and brackish) is the most dense and why? Least dense: Middle: When the three colors layered which was on the Top? Middle? Bottom? 4. Now label the fresh water, brackish water and ocean water. Explain why they are layered as they are. 5. Experiment with making a density current in the straw. 19

20 Explanation: Density is mass divided by volume. In this activity we used the same volume of solution each time, but since there is a different mass of salt dissolved in each solution, the density of the solutions are different. More salt was dissolved in the ocean (blue) water making it the most dense of the three. Less salt was dissolved in the brackish (red) water. No salt was dissolved in the fresh (green) water, making it the least dense of the three. When layered ocean, brackish, fresh -- with ocean on the bottom -- the layers stayed distinct. Density currents are visible if a more dense solution is added after a less dense solution (for example, ocean after fresh). Convection in the Ocean Activity #2 Purpose: To observe how changes in water temperature cause convection currents. Materials: Blue ice cubes (made ahead of time with blue food coloring) One clear, colorless plastic container (about shoebox size) Red food coloring warmed Note: To warm put container of food coloring in a cup of hot - not boiling - water. Blue and red colored pencils Index cards Procedure: 1. Fill the container two-thirds full of room temperature water. Make sure the water is completely still before proceeding. 2. Place a blue ice cube at one end of the plastic container. 3. Add two drops of the warmed red food coloring at the other end of the container. 5. Observe, and use the blue and red pencils to illustrate, on the index card, what you see happening. 20

21 Explanation: Convection is apparent as the blue (cold) water sinks, and the red (warm) water rises, or stays higher. If this cold water was also salty (like sea water at the poles) can you see that it would be even more dense?! 21

22 Day 9 - Convection in the Sun and Earth's Mantle Concepts: We think of the earth as a solid, but really the solid crust is riding on top of the earth's mantle. The mantle is a viscoelastic fluid, like Silly Putty. If you hit Silly Putty with a hammer, it breaks like a rock. If you slowly pull Silly Putty, it will stretch. If you leave Silly Putty hanging slightly over the edge of a table, it will slowly flow downward. The solid crust is mostly granitic and basaltic rock which "floats" on the more dense molten iron and magnesium rocks of the mantle. Beneath the mantle is the extremely hot core with temperatures greater than 6,000 degrees Celsius. The Earth's crust is not one solid piece of rock, but is made up of what scientists call plates. These plates are not stationary. It is their movement and resulting seismic activity that indicates convection currents in the Earth's mantle. Convection also occurs in the Sun which is made up of a fluid called gas plasma. There is a layer of the sun called the Convective Zone. 22

23 Convection in the Earth s Mantle Activity Purpose: To simulate convection in the Earth's mantle. Keep in mind convection in the Earth's mantle occurs VERY slowly - over millions of years! Materials: Piece of paper Four Styrofoam cups Hot and cold water Food coloring (any color) Eye dropper Clear plastic plant saucer (8-10 inches. Ridges that are concentric circles won't work; radial rides are okay.) Procedure: 1. Place three Styrofoam cups upside down on a piece of paper. 2. Put the plastic saucer on top of the cups. The cups should be evenly spaced near the outer edge of the saucer. 3. Fill the plastic saucer 3/4 full with room temperature water. Wait until the water is perfectly still before proceeding. The water should remain motionless throughout the experiment. 4. Fill the eyedropper with a few drops of food coloring. 5. Release the color in the water right at the bottom of the plastic saucer. 6. Slowly remove the dropper, being careful not to stir the water. 7. Observe and record what the color does 23

24 8. Dump out the water in the saucer and repeat steps 2 through 7 with the following variation: Place a totally full cup of hot water under the center of the plastic saucer, and then add a few drops of color in the water right at the bottom of the plastic saucer. Explanation: The hot wa ter causes the food color to warm and move upwa rd through the liquid, simulating the co n ve ction current in the Earth's mantle. 24

25 Day 1O - Wrap-up Assessment: Hot air balloons have been prominent throughout the television series, and in this activity guide. Clearly convection enables hot air balloons to work. On this Assessment Worksheet label what is enabling the "Balloon on the Rise" to go up, and what is enabling the "Balloon on its Way Down" to sink. Consider the temperature and density of the air inside the balloon; consider air pressure inside the balloon; and consider the buoyancy of the balloon. How do these things change in relation to the air outside of the balloon as the balloon goes up, and as the balloon sinks? Balloon on the Rise Balloon on its way Down CONGRATULATIONS! You've now made the convection connection!! 25

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