Convection Cells Gizmo Answer Key

Name: Matilda Kramer Date: 05-01-2022 Student Exploration: Convection Cells Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. Vocabulary: convection, convection cell, density, global conveyor belt, mantle, mid-ocean ridge, subduction zone, vector, viscosity Prior Knowledge Questions (Do these BEFORE using the Gizmo.) You place a pot of soup on the stove. As the soup warms you notice some areas where soup is rising up and other areas where soup is sinking down. 1. Why do you think some of the soup is rising up? I believe that some of the soup is rising due of the pressure of the hot air. 2. Why do you think some of the soup is sinking down? The soup is sinking because the temperature is colder. Gizmo Warm-up When fluids (gases or liquids) are heated, they tend to move. This motion is called convection. In the Convection Cells Gizmo, you will observe and experiment with convection both in a laboratory setting and in several real-world examples. To begin, note the laboratory setup on the MODEL tab. A beaker of liquid is placed above a gas burner. Click Play ( ). The burner is now heating the fluid. 1. What do you notice? Moving in a circular motion 2. Drag the eyedropper into the beaker just above the burner and let go to release a drop of orange liquid into the beaker. What do you notice about the path of the drop? The drop's trajectory is circular. Activity A: Get the Gizmo ready: Convection ● Click Reset ( ), and set Burner A to High. Question: What causes convection cells to form? 1. Hypothesize: Click Play, add a drop, and watch the motion of the liquid. Why do you think convection tends to occur in heated fluids? because it circulates and begins to move when it is heated. 2. Observe: Click Clear drop. Under Show, select Temperature. The temperature scale runs from red (hot) to dark blue (colder). A. Where is the hottest liquid located? at the base nearest the flames B. Where is the coldest liquid located? in the corners farthest from the fire. C. Add a drop. Does the hottest liquid tend to rise or sink? It usually increases. D. Does the coldest liquid tend to rise or sink? It usually sinks. 3. Observe: Click Clear drop, and then add a new drop to the liquid. Turn on Show micro view of drop. This view shows 21 molecules in the drop. Pay attention to how fast the molecules move and how much space they occupy as the drop moves around the beaker. (Note: If the drop gets stuck, add a new drop to the beaker.) A. In which part of the beaker do the liquid molecules move fastest? closest to the flame B. In which part are the liquid molecules most spread out? most near the beaker. 4. Explore: Click Clear drop and drag the probe ( ) into the beaker. Density is defined as the mass per unit volume. It is a measure of how tightly the particles of a substance are packed. Move the probe to different parts of the beaker, observing the temperature and density. A. What relationship do you observe between the temperature and density? As the temperature rises, the liquid becomes denser. B. Why do you think this is so? I believe the density is the reason of this. 5. Explain: In a liquid, objects denser than the liquid (such as rocks) tend to sink, while objects less dense than the liquid (such as inflatable rafts) tend to rise. How does this relate to the observed motions of the liquid in the beaker? The beaker's liquid is denser than the other liquid because of the temperature. Convection occurs because heated fluids become less dense, causing them to rise. Cooled fluids become denser, causing them to sink. 6. Observe: Click Reset. Select Motion and turn on Show velocity vectors. Click Play. The vectors (arrows) show the speed and direction of the liquid at each point in the beaker. A. What is the general pattern of motion? This circulation is known as a convection cell. In a convection cell, hotter fluid rises while cooler fluid sinks. it is moving in a circular motion B. Why do you think the liquid in the bottom of the beaker moves to the left, while liquid at the top of the beaker moves to the right? due to the variation in density. In the convection cell, liquid moves horizontally because it is pushed by other liquid. The liquid at the top of the beaker moves to the right because it is pushed by the rising liquid on the left. The liquid at the bottom of the container is pushed to the left by the downward-moving liquid on the right. The whole beaker is a closed system, so liquid motion in one part of the beaker must be offset by liquid motion elsewhere. 7. Summarize: In your own words, describe what causes convection to happen and what causes convection cells to form. The warmer, less dense portion of the liquid rises because the colder, denser portion sinks underneath it. Activity B: Get the Gizmo ready: Factors that affect convection ● Click Reset. Set Burner A to High. ● Turn on Advanced features. Question: What factors affect the characteristics of convection cells? ✏️ 1. Predict: For each of the configurations below, predict what the convection cell (or cells) will look like. Draw a sketch with arrows showing the motion of the liquid in each diagram. (Note there are two burners in the right-hand image.) Hand draw in each space or click to select EDIT to use the drawing tool. ✏️ 2. Test: Use the Gizmo to model each scenario by dragging the burner left or right. In each case, set the burner to High. For the two-burner simulation, turn on Advanced features and select Add a second sketch the burner. For best results, set the Viscosity to 0.0 m2/s. Turn on Show velocity vectors and results, then explain why the liquid moves as it does. ) Hand draw in each space or click to select EDIT to use the drawing tool. ✏️ ✏️ 3. Experiment: Click Reset. Turn off the second burner and move burner A to the left side of the beaker. Experiment with the four burner settings to determine how the amount of heat affects the speed of the liquid. What did you find? When the burner is moved, the arrows also move. 4. Explain: Why doesn’t a convection cell form when the burner is turned off? because there isn't an increase in temperature. 5. Experiment: The viscosity of a liquid is its resistance to flow. Ketchup and honey, for example, have a greater viscosity than water. Experiment with different Liquid viscosity values to determine how viscosity affects the speed of the liquid in the convection cell. Describe your findings: the more dense a liquid is, the higher the viscosity. 6. Explain: Move burner A as far as it can go to the left and set it to High. Set the Liquid viscosity to 0.2 m2/s. Turn on Burner B and set it to Medium. Move this burner as far to the left as possible, next to Burner A. Select Show temperature and click Play. In this setting, you should get a large contrast between the hottest and coolest parts of the beaker. A. Use the eyedropper to add a drop and turn on Show micro view of drop. How does the speed of the molecules in the drop change as the drop goes around? it increases B. How does this affect the size and density of the drop? Because there is more room inside the molecules, the density falls. C. What causes the drop to move around the container? The warmth inside the beaker causes the liquid to swirl inside the beaker, which causes the drop to move. Activity C: Real-world convection Get the Gizmo ready: ● Select the EXAMPLES tab. ● Check that Mantle is selected. Introduction: The convection you observe in the lab (or in a pot of soup on the stove) also occurs on much larger scales. In this activity, you will learn about four types of convection cells that form on Earth. Question: Where does convection occur on Earth? 1. Observe: Earth’s mantle is a zone of semi-molten rock, or magma, found between the solid crust that makes up Earth’s surface and the molten rock in Earth’s outer core. Read about mantle convection, then click Play to observe convection cells in the mantle. What is the general pattern of magma circulation in the mantle? It moves in a circle. 2. Describe: Click the central orange dot to learn more about mid-ocean ridges. A. What occurs along a mid-ocean ridge? Tectonic plates disperse B. Click the right-hand dot to learn about a subduction zone. What occurs at subduction zones? friction between the continental lithosphere and oceanic crust. C. The country of Japan is located along a subduction zone between the Philippine Plate and the Eurasian Plate. What natural disasters might be common in Japan? earthquakes and tsunamis 3. Observe: Select Ocean. The global conveyor belt is a vast, slow-moving convection cell that connects Earth’s oceans. Click each of the orange dots to read about what causes water to move up and down in the global conveyor belt. A. What two reasons cause water to move downward in the North Sea? Water sinks to the ocean floor as a result of cooling and becoming denser due to heat loss to the atmosphere. B. What causes water to rise near the equator? the density levels. 4. Infer: Why might a zone of upwelling be a good place to fish? because the high temperatures frequently draw fish there. 5. Observe: Select Coast and read about and observe convection cells that occur in the air around coastlines. Select each orange dot and see what happens during the day and night. A. If you are standing on a beach, why might you feel an ocean breeze during the day? because land and water heat up at different rates. B. If you are starting a sea voyage in a sailing ship, why would it be a good idea to leave shore at night? because there is a heavy flow of wind C. What causes the direction of the wind to change from day to night? external cooling 6. Observe: Select Atmosphere. The atmosphere contains three large-scale convection cells. Click Play to observe these cells, and then select each orange dot to learn more. A. What causes air to rise near the equator? heat rises and the temperature is warmer near the equator. B. What causes air to sink near the latitude 30° N (and 30° S)? cold air sinks C. Why are climates generally wet near the equator, and generally dry around the latitudes 30° N and 30° S? due to the humidity and rising temperatures,