Convection Current and Tectonic Plates

Transcription

1 Convection Current and Tectonic Plates 9 th -12 th Grade Standards: This activity meets California science standards for grades 7 through 12. Purpose: Students should understand the actions of fluids and gases with varying densities, which create convection currents. This demonstration will broaden their understanding of how such currents shape the face of the Earth. Materials Needed: 1. Large clear rectangular tub. 2. Five (5) Styrofoam cups. 3. Cardboard. Four 4 x4 squares. 4. Hot water. (Near boiling). 5. Several ice cubes. 6. Food coloring. One or more colors. 7. Dropper or pipet with long neck. Question for the students: Why does warm air rise? Does the same thing happen with water? Procedure: 1. Place four of the Styrofoam cups on a table in a rectangle slightly smaller than the dimensions of the tub. 2. Place one of the 4x4 cardboard pieces under each cup. 3. Place tub on the four elevated cups, ensuring that the tub is evenly balanced. 4. Fill tub ¾ s of the way with cold tap water. 5. Using a pipet or dropper, gently deposit a 1-2 blob of food coloring at the bottom of one edge of the tub. 6. Fill the fifth cup with hot water and place it directly under the blob of food coloring. 7. Watch and wait for the food coloring to start rising.as the food coloring reaches the surface, gently float an ice cube in the opposite side of the tub. tech/node76.html

2 Conclusion: The food coloring makes it possible to visualize the convection current moving in the water. The heat transfers from the cup to the plastic to the water and rises to the surface. The ice cube helps the process along by increasing the temperature gradient between the top and bottom of the tub. Anything floating on the surface of the water will also move with the current. Try setting a leaf or a piece of paper on the surface to see this in action. Now imagine huge tectonic plates being pushed along by similar forces within the mantle of the Earth! Questions: In what other systems does convection current take place? (It occurs in fluids, and air is a fluid too!) Discussion: What does convection current mean for the geography of our planet? The commonly accepted theory is that convection current in the mantle of Earth is the driving force of tectonic activity.

3 Name: WORKSHEET: CONVECTION CURRENT Instructions: Draw a model of the density of water molecules in the circles labeled Colder water and Warmer water. The density can be portrayed by drawing smaller circles, like those shown below, in relatively more or less dense patches. Use arrows to show the direction the water is flowing. These arrows should form a circle that shows which way the convection current is flowing. Colder water Warmer water

4 Teachers Resources: Vocabulary: 1. Density: Mass per volume. 2. Convection current: Current induced by a difference in the temperature (temperature gradient) of liquids and gasses. 3. Convection: movement of molecules within fluids (liquids and gasses). 4. Tectonic plate: A landmass that composes part of the crust of the Earth and is always in motion, driven by convection current of the mantle of the earth. Material Notes: 1. Use the longest-necked pipette or dropper you can find. It will minimize disturbing the water. 2. Pick a darker food coloring and remember that yellow looks awkward. 3. Styrofoam cups work best, because they are designed to handle hot liquids. Paper coffee cups would also work, although some may not be strong enough to support the tub of water. Activity Notes: The Science: 1. The key is to be as gentle as possible when dealing with the water in the tub. Try not to disturb the water when placing the food coloring or ice cube, because outside influences make it hard to see what is happening in the water As materials warm, their density (mass per volume) decreases. Conversely, as materials cool, their density increases. Low-density material rises and high-density material sinks. By increasing the temperature at the bottom of the tub, the material cycles up and down as it warms and cools at the bottom and top of the tub. This cycle is called convection current. Tectonic plates that sit on the mantle move slowly (millimeters to centimeters a year), pushed by the convection currents in the mantle.

5 Standards: California Science Framework, Physics Standard Set 1: Motion and Forces b. When forces are balanced, no acceleration occurs. Standard Set 3: Heat and Thermodynamics a. Energy cannot be created or destroyed. Heat flow and work are two forms of energy transfer between systems. c. The internal energy of an object includes the energy of random motion of the object s atoms and molecules, often referred to as thermal energy. The greater the temperature of the object, the greater the energy of motion of the atoms and molecules that make up the object. d. Most processes tend to decrease the order of a system over time and that energy levels are eventually distributed uniformly. Answer Key: Warmer Water Colder Water The arrows should point counter-clockwise. Hot water rises and then falls when it cools. References: Community Science Action Guides. (2011). The Secret Live of Energy, The Energy Solution. Convection, < (Aug 2011)

6 Kobes and Kunstatte. (1999). Convection. Convection currents, < (Aug. 2011)