Heat and Density Grade Nine

Transcription

1 Ohio Standards Connection: Earth and Space Science Benchmark E Explain the processes that move and shape Earth s surface. Indicator 5 Explain how the slow movement of material within Earth results from: a. thermal energy transfer (conduction and convection) from the deep interior; b. the action of gravitational forces on regions of different density. Related Benchmarks and Indicators Physical Science Benchmark C Describe the identifiable physical properties of substances (e.g., color, hardness, conductivity, density, concentration and ductility). Explain how changes in these properties can occur without changing the chemical nature of the substance. Indicator 9 Investigate the properties of pure substances and mixtures (e.g., density, conductivity, hardness, properties of alloys, superconductors and semiconductors). Lesson Summary: Students will be introduced to the concepts of density and convection/conduction through demonstrations, notes and activities. Students will use physical models to gain understanding of the processes that move and shape the Earth s surface. Estimated Duration: Three to four hours Commentary: This lesson is designed to use real-world examples to model the processes that move and shape Earth s surface. After experimenting with concrete models, students will be required to evaluate the successes and limitations of using the systems to model the Earth system. This lesson was reviewed by educators across the state of Ohio. Some of their comments were: The lesson starter was efficient in getting the students to start thinking. I liked how the lesson takes into account each type of learner and involved each student. The objects used in demonstrations and examples were very real for my students. Pre-Assessment: Perform the following three demonstrations: 1. Add macaroni to water, boiling in a beaker. 2. Add raisins to clear pop in a beaker. 3. Display a commercial lava lamp. Ask students to write explanations of the demonstrations in their journals. 1

2 Scientific Inquiry Benchmark A Participate in and apply the processes of scientific investigation to create models and to design, conduct, evaluate and communicate the results of these investigations. Indicator 3 Construct, interpret and apply physical and conceptual models that represent or explain systems, objects, events or concepts. Heat and Density Grade Nine Scoring Guidelines: Evaluate the responses to determine the level of understanding as well as misconception students may have about convection. Use the information gathered to guide instruction throughout the lesson. The following are examples of possible responses. 1. The water at the bottom of the beaker is warmed from the heat source. As the water warms, it expands, becomes less dense and rises to the top. At the top, the water cools, becomes denser and falls to the bottom. Denser materials settle below less dense materials because the gravitational force on them is greater. The gravitational force is greater because it is proportional to the mass of the material, and materials with greater density have more mass per unit volume than materials with lower density. This cycle sets up convection currents within the water which can be observed when the macaroni is added. 2. Clear pop is a carbonated beverage, which means carbon dioxide gas is dissolved in it. When the pop s top is removed and it gradually warms, the gas is released as small bubbles, which rise to the top. When a raisin is added, it starts falling to the bottom because it is denser than the liquid; but as it falls, bubbles of gas form around it causing the density (of the raisin and attached gas) to be less than the liquid, so it rises to the top. When the gas bubbles escape out of the liquid, the raisin falls again. The cycle repeats itself as long as bubbles of carbon dioxide are released. 3. The lava lamp is made of two different liquids. Like oil and water, the "lava" in a lava lamp doesn't mix with the liquid that surrounds it. When it's cool, the "lava" is denser than the liquid surrounding it, so it falls to the bottom of the lava lamp. When the light bulb in the lamp warms it, the "lava" expands. When it expands, the "lava" has the same mass but it takes up more space; therefore, it is less dense than it was at the cooler temperature. When it's warm enough, the "lava" is less dense than the surrounding liquid, so it rises to the top and floats. At the top of the lamp, it cools, becomes denser and sinks once again. This cycle repeats as the "lava" warms up and rises, then cools and sinks. Post-Assessment: Ask students to evaluate a drawing of the Earth showing various plate boundaries (divergent and convergent) by labeling a diagram of plate boundaries and describing what is occurring in terms of energy transfer and gravitational forces. See Attachment C, Post-Assessment. Scoring Guideline: See Attachment D, Post-Assessment Answers. 2

3 Instructional Procedures: 1. Have students explore the topic of plate tectonics and the location of various plate boundaries, using a science textbook and other resources (videos, Web sites, CD-ROMs, etc.). 2. Perform the following demonstration on density: a. Display a large graduated cylinder and the following items: salt water, light corn syrup, vegetable oil, lead sinker, plastic cube (like a number cube) and a cork. Ask the students to think about the level at which each item will settle if all of the items are added to the graduated cylinder. Ask them to make drawings showing their predictions and to write explanations justifying their predictions. b. Add the items to the graduated cylinder in any order. Ask students to write what they observe as well as any questions they have about the demonstration. 3. Before beginning the Density Lab (See Attachment A, Density Lab), discuss with students the density formula (D = m/v). Ask the following questions: a. What does D represent? b. What does m represent? c. How can you measure m (with which tools)? d. What does V represent? e. How can you measure V (with which tools)? 4. In this lab, students calculate the densities of the items in the original graduated cylinder demonstration described above. They predict relative positions of the items based on their calculated densities and then repeat the filling of the graduated cylinder to see if their predictions are correct. 5. Instruct students to record measurements and answers to questions in their lab notebooks. 6. After the completion of the lab, conduct a whole-class discussion about the results of the lab and the questions that were asked. 7. Provide notes on plate boundaries, gravitational forces, density and thermal energy transfer. 8. Repeat the same convection demonstrations from the pre-assessment. Talk about and have students diagram the movement of the liquids as the temperature within the container varies. 9. Display the filled graduated cylinder from the demonstration or from the density lab. Conduct a class discussion to ensure that students understand the successes and limitations of using the system to model the Earth system. 10. Demonstrate a homemade lava lamp. See instructions for making the lava lamp in Attachment B, Lava Lamp. Instructional Tip: The materials used in the lava lamp are flammable--use caution when applying heat. 11. In pairs or small groups, have students discuss the homemade lava lamp to explain how it was made and how it models processes within the Earth. Have students list successes and limitations of using the lamp as a model of Earth systems. See Attachment B, Lava Lamp for Discussion Questions. 3

4 12. Conduct a whole-class discussion where students share the ideas that were generated within their small group discussions. Ensure that students understand the successes and limitations of using the lava lamp to model Earth processes. Differentiated Instructional Support: Instruction is differentiated according to learner needs, to help all learners either meet the intent of the specified indicator(s) or, if the indicator is already met, to advance beyond the specified indicator(s). Place students in heterogeneous groups that respond to students differing skills, knowledge, experience, etc. Before beginning the Density Lab, discuss with students the density formula D = m/v and reinforce concepts with visual representation, notes, graphic organizer, etc. Challenge students to investigate various liquids and solids to make their own convection containers. Extensions: Have students research volcanic eruptions or earthquakes and explain how these relate to thermal energy transfer from the deep interior of the Earth and the action of gravitational forces on regions of different density. Have students experiment with various liquids and solids to make their own convection containers. Homework Options and Home Connections: Have students look for examples of conduction and convection in their homes. Materials and Resources: The inclusion of a specific resource in any lesson formulated by the Ohio Department of Education should not be interpreted as an endorsement of that particular resource, or any of its contents, by the Ohio Department of Education. The Ohio Department of Education does not endorse any particular resource. The Web addresses listed are for a given site s main page, therefore, it may be necessary to search within that site to find the specific information required for a given lesson. Please note that information published on the Internet changes over time, therefore the links provided may no longer contain the specific information related to a given lesson. Teachers are advised to preview all sites before using them with students. For the teacher: Macaroni, clear pop, raisins, commercial lava lamp, graduated cylinder, pan balance, metric ruler, salt water, light corn syrup, vegetable oil, lead sinker, plastic number cubes, cork, mineral oil, rubbing alcohol, tall jar (about 10 inches) with lid, desk lamp with 40-watt light bulb, ring stand with two rings and mesh. 4

5 For the students: For the density lab: graduated cylinder, pan balance, metric ruler, salt water, light corn syrup, vegetable oil, lead sinker, plastic number cube, cork. Vocabulary: thermal energy conduction convection gravitational forces density plate tectonics plate boundary divergent boundary convergent boundary continental drift Technology Connections: Use the Internet to access information about plate tectonics and the location of various plate boundaries. A good Web site is the United States Geological Survey (USGS). Research Connections: Marzano, R., et al. Classroom Instruction that Works: Research-Based Strategies for Increasing Student Achievement, Alexandria, VA: Association for Supervision and Curriculum Development, Nonlinguistic representations help students think about and recall knowledge. They include the following: Creating graphic representations (organizers); Making physical models; Generating mental pictures Drawing pictures and pictographs; Engaging in kinesthetic activity. Cooperative learning has a powerful effect on student learning. This type of grouping includes the following elements: Positive interdependence; Face-to-face promotive interaction; Individual and group accountability; Interpersonal and small-group skills; Group processing. 5

6 Attachments: Attachment A, Density Lab Attachment B, Lava Lamp Attachment C, Post-Assessment Attachment D, Post-Assessment Answers 6

7 Attachment A Lab: Density Materials: graduated cylinder, pan balance, metric ruler, salt water, light corn syrup, vegetable oil, lead sinker, plastic number cubes and cork. Procedures: 1. Thinking back to the demonstration you saw earlier, list, to the best of your ability (from your memory of the demonstration and your own knowledge), the materials in order from least dense to most dense. 2. Find the mass of the graduated cylinder and record this number in your lab book. 3. Add some salt water to the graduated cylinder and record its volume in your lab book. 4. Find the mass of the salt water. What should you do to find this? Record the salt water s mass in your lab book. 5. Using the data you have obtained (salt water volume and mass), determine the salt water s density. How did you do this? 6. Determine the mass, volume and density of all of the liquids in the same manner you have done with the salt water. 7. Find the mass of the number cube. Record this number in your lab book. 8. Find the volume of the number cube by measuring its length, width and height and multiplying these numbers together. Record this number in your lab book. 9. Determine the density of the number cube as you did with the liquid and record this number in your lab book. 10. Determine the mass, volume and density of the lead sinker and cork. Their volumes may be determined by doing the following: Place 20 ml of tap water in the graduated cylinder. Add the item to be measured (sinker or cork). Determine how much the water has risen. (Be sure to submerge the cork.) This is the volume of the item you are measuring. 11. Now that you have density numbers for each item, write a new prediction about the order of the items when placed in the graduated cylinder. 12. Put all of the items in the graduated cylinder. How accurate was your prediction? Which prediction was more accurate, the one before or after you calculated the items densities? 13. Draw a picture of the graduated cylinder and the items in it. 14. Answer the questions. Questions: 1. In your own words, explain density or draw a picture to explain it. 2. It is thought that there is liquid under the crust of the Earth. What would you expect to happen to liquids of various densities here? Why? 3. Under the crust, what does gravity do to materials of different densities? Explain. 7

8 Attachment A (continued) Lab: Density Key to Questions: 1. Student responses will vary, but they should indicate that density represents the mass of a unit volume of a material. 2. Liquids of different densities would be set into motion (circulate) relative to one another. The end result of the motion would be liquids of lower density settling above the liquids of higher density under the crust because of the effect of gravity acting on them. 3. The gravitational force on materials is proportional to the mass of the material. Since materials with greater density have more mass per unit volume than materials with lower density, the gravitational force per unit volume is greater on materials of greater density. Under the crust, volumes of higher density material move to lower levels because of the greater gravitational force. 8

9 Attachment B Lava Lamp Materials: mineral oil rubbing alcohol (isopropyl alcohol) diluted to 70 percent and 90 percent tall jar (about 10 inches) and lid desk lamp and 40 watt light bulb ring stand with two rings and mesh graduated cylinder Procedure: 1. Fill one-third of the jar with 90 percent alcohol. 2. Add 20 ml of mineral oil. 3. Slowly add 70 percent alcohol to the jar, gently mixing. Do this until the oil seems lighter and is about to jump off the bottom. Use the two alcohols to adjust the responsiveness of the "lava." More of the 70 percent alcohol is needed than the 90 percent 4. Put the lid on the jar and tighten it. 5. Place the jar on the mesh (which should be situated on the lower ring of the ring stand) and through the upper ring of the ring stand so that it is secure. 6. Place the lamp under the jar and turn it on. 7. Wait several minutes, then record your observations. After five minutes, if nothing has occurred, you may try several suggestions: adjust the lamp so that it is closer to the jar, agitate the jar so that the mineral oil forms small bubbles or start again, but reduce the alcohol concentration. Discussion Questions: 1. Write your observations after watching the lamp for at least 10 minutes. 2. Make a diagram of what you observed with the lamp. 3. Define: density, gravity, convection and conduction. 4. Explain what is happening in the lava lamp in terms of density, gravity, convection and conduction. 9

10 Attachment B (continued) Lava Lamp Key to Questions: 1. Answers will vary. 2. Answers will vary. 3. Density: The amount of mass in a given volume. Gravity: The gravitational attraction of the mass of the Earth, the moon or a planet for bodies at or near its surface. Convection: The circulatory motion that occurs in a fluid at a non-uniform temperature owing to the variation of its density and the action of gravity. Conduction: Process by which heat or electricity is transmitted through a material or body without movement of the medium itself. 4. The lava lamp is made of two different liquids. Like oil and water, the "lava" in a lava lamp doesn't mix with the liquid that surrounds it. When it's cool, the "lava" is denser than the liquid surrounding it, so it falls to the bottom of the lava lamp. When the light bulb in the lamp warms it, the "lava" expands. When it expands, the "lava" has the same mass but it takes up more space; therefore, it is less dense than it was at the cooler temperature. When it's warm enough, the "lava" is less dense than the surrounding liquid, so it rises to the top and floats. At the top of the lamp, it cools, becomes denser and sinks once again. This cycle repeats as the "lava" warms up and rises, then cools and sinks. This process sets up convection currents. Denser liquids sink because they are more massive per unit volume, so the gravitational force on them is greater. The gravitational force is greater because the force of gravity is proportional to the mass of the material, and materials with greater density have more mass per unit volume than materials with lower density. The liquid at the bottom of the container warms up through the process of conduction as heat is transferred from the hot glass to the liquid through direct contact. The liquid at the top also cools by conduction because heat is transferred from the liquid to the air. 10

11 Attachment C Post-Assessment Cross section drawing by José F. Vigil from This Dynamic Planet -- a wall map produced jointly by the U.S. Geological Survey, the Smithsonian Institution, and the U.S. Naval Research Laboratory. 1. What is happening at the hot spot? Explain why this is occurring in terms of energy transfer and gravitational forces. 2. What is happening at the oceanic spreading ridge? Explain why this is occurring in terms of energy transfer and gravitational forces. 3. What is happening at the continental rift zone? Explain why this is occurring in terms of energy transfer and gravitational forces. 4. What is happening at the subducting zone? Explain why this is occurring in terms of energy transfer and gravitational forces. 5. What is happening to the earth s continents? 6. What would change if there were no energy transfer occurring? 7. On the above diagram, label the regions described in questions one through four with the number of the question. 11

12 Attachment D Post-Assessment Answers The following answers are provided as background information for the teacher. Appropriate student responses will depend on the depth of instruction as students work toward or beyond the indicator. 1. Hot spots are formed directly from columns of hot mantle rock rising from the convective heat below the asthenosphere. These mantle plumes rise to the lower pressure environment of the lithosphere and partially melt the rock to form pockets of localized volcanism. The Hawaiian Islands provide an excellent example of this process. Heat convection accounts for the energy transfer in a hot spot and the change in rock density due to the physical change from solid to partially melted material reduces the gravitational force acting on it. 2. Oceanic crust is much thinner in some locations, causing an intense interaction with mantle plumes similar to the cause of hot spots, only at a much greater level, causing the seafloor to spread. Heat convection causes an upwelling of magma, which actually breaks the surface of the sea floor, causing rift zones with transform faulting on either side of the rift. As the upwelling fills the newly formed fault fractures, the oceanic plates are pushed apart allowing for more magma to rise and to continue the process that is sometimes modeled by a conveyor belt. The energy transfer is caused by heat convection from within the mantle, and the gravitational forces aid the conveyor-like process in combination with the upwelling and faulting. 3. Continental rift zones occur very similarly to mid-ocean rifting. An upwelling mantle plume causes a doming effect to the continental crust directly above it. As the dome increases, extensional forces stretch and thin the crust followed by faulting and localized volcanism. Along the spreading axis, down-faulting occurs and a rift valley is formed. As the spreading continues, the rift valley grows longer, deeper and wider, becoming narrow seas that usually extend to the oceans. Doming often forms a triple junction, where rifting occurs in three directions, extending from the center of the dome. An excellent example of this is the East African Rift, which shows the Red Sea, Gulf of Arden and Lake Victoria and Lake Tanganyika as the triple rifts. The energy transfer is by convective heat currents that cause the doming and lithospheric thinning. The gravitational forces cause the sinking of the rift by down-faulting and the influx of water filling the valley, as well as the spreading process itself. 4. As spreading occurs at the mid-ocean ridges, plates are pushed toward one another causing collision. These plate collisions are called convergent boundaries. When oceanic crust converges onto continental crust, by means of sea floor spreading, subduction occurs. Subduction is the movement of the more dense basaltic rock of oceanic crust below the less dense granitic rock of continental crust. As a result, earthquakes occur along the subduction zone and island arc or magmatic arc volcanism 12

13 Attachment D (continued) Post-Assessment Answers occurs inland above the zone of partial melting from the subducting oceanic crust. The energy transfer begins at the spreading rift zones and transfers to the geologic hazards in the form of earthquakes and volcanoes during subduction. The gravitational forces act on the subducting plate as well as the regions of different lithologic composition with different densities between the plates. 5. Continental crust is currently being resurfaced, destroyed and created. Different boundaries cause different changes to the surface of the earth. Convergent boundaries are boundaries that destroy oceanic crust through subduction and cause volcanism and faulting on the surface of continental crust. When two continental plates converge, buckling, folding, fracturing and uplift occur to form mountains and disturbed rock layers. Once this occurs, erosion takes place and sediment deposition occurs. The rock cycle, along with the processes of plate tectonics, completely renews the surface of the earth over great periods of geologic time. As these surfaces change, they again head for collision into one another. Just as the super continent Pangaea broke apart during the Permian, so will it return once again to a solid mass of continental crust through the destructive and constructive processes of plate tectonics. 6. The world as we know it would not exist if there were no energy transfer. Physically speaking, there would be no heat convection, no plate movement, no weathering or erosion and no magnetic field to protect us from the sun s destructive rays. 13