Mark Schain - Convection Currents

Tea Bag Rocket

Natural ConvectionPrinciple(s) Investigated: The principles that apply to this activity are as follows:

1. Two types of convection will be investigated, natural and forced convection

2. There are two types of media in which convection occurs: liquid or gas.

3. Thermal updrafts contribute to the formation of convection cells/currents.

Standards: Energy in the Earth’s Systems:

The transfer of energy through convection currents and radiation are believed to influence the geologic events that occur on Earth’s surface.

4.c Convection is the main cause to which heat in the center of the earth reaches the surface of the earth

4.d The heat that exists in the Earth’s atmosphere and oceans is distributed by convection currents

Materials:

1. Metal pie tin or ceramic bowl

2. Wooden matches or butane lighter

3. Scissors

4. Tea Bag

5. Plastic spray bottle

6. 1 Large Ziplock bag (for storage of supplies)

7. 1 Small Ziplock bag (for disposal of trash)

Procedure:

· NOTE: Make sure that there is nothing flammable in the room within a six-foot radius of where you are working. Place a spray bottle filled with water on the experiment table within arms-distance to where you are working. Close all doors and windows to prevent any breezes or cross ventilation from interfering with the experiment.

· Show and discuss the first part of the power point presentation with students, which introduces the Need To Know discrepant event

· Pass out lab sheets to students

· Think-Pair-Share Activity: Encourage students to

work in pairs or cooperative groups to write a response to the first question on the lab sheet. Ask students to share their responses with the class

· Continue the power point presentation, discussing the scientific principle of convection.

· Experiment (teacher conducted): Demonstrate The Tea Bag Rocket experiment progressing through the following steps:

· Open the large plastic bag and remove all contents.

· Remove small plastic bag and open to put all debris in.

· Unfold the tea bag and cut top of tea bag off with scissors. Empty contents into the tin or bowl.

· Tea grounds will be used to support the fabric chimney.

· Open up empty tea bag into its cylinder shape (both ends cut off) and stand up vertically, embedding one end into the tea grounds.

· Strike match or light lighter to ignite the top of tea bag. The tea bag will burn to the bottom. There will be thermal updraft and the ashes from the burned tea bag will lift into the air, illustrating the presence of convection currents and the direction of movement.

· When the experiment is finished, make sure that all debris is placed in small bag and that all other materials are placed into large bag.

· Experiment (student conducted): Students repeat the experiment with teacher guidance.

· In pairs or cooperative groups, students write their responses from the second question from the lab sheet.

· Evaluation: Ask students to share their written responses with the class. Observe the appropriate use of academic vocabulary related to the science concepts presented, as well as the understanding of the scientific principles taught.

Student Prior Knowledge:· Students will need to know that density is how close together the molecules of an object are to each other

· Students will need to know that temperature can affect the density of an object

Explanation:

•Convection currents form because of differences in density.

•Less dense materials rise because their molecules are farther apart from each other. The introduction of heat excites the molecules, forcing them farther and farther a part. When the molecules get far enough apart, they become lighter than the surrounding liquid or gas and rise.

•More dense materials sink because they are heavier than the surrounding liquid or gas. They can be denser as a result of temperature or denser because of their molecular properties. An example of this would be carbon dioxide obtained from dry ice submerged in water. This gas is heavier than air and therefore, sinks.

Natural Convection:

•Natural convection: The movement of air from hot to cold in a circular motion driven by differences in density and pressure. Your fireplace and attached chimney creates natural convection when it uses a natural heat source such as wood or natural gas to heat the air just above the heat source. The super heated air rises up, due to its decreased density, and draws the smoke up with it. This natural movement of hot and cold air and the direction in which this gas flows is natural convection. Forced Convection:

Forced Convection:

•Forced Convection: The movement of air from hot to cold in a circular motion driven by mechanical forces.When you dry your clothes in the dryer, either a heating element inside your electric dryer or natural gas heats up the air above the heat source. An electrical fan pushes the air into a drum, heating up the water - soaked clothes, causing the water to evaporate and your clothes to dry. When you dry your hair with your hair dryer, the heat that is generated is produced by an electric filament, which heats up the surrounding cold air. The newly heated air is forced out of the hair dryer, heating up your water - soaked hair, causing the water to evaporate and your hair to dry. Explanation:

This experiment demonstrates natural convection because as the tea bag burns, the molecules of air become hotter and hotter. These super heated molecules expand and become less dense than the surrounding air. The air above the heat source begins to rise. As the hot air rises, so do the ashes because they are very light and begin to ascend with the updraft. The surrounding cold air rushes in to take the place of the hot air. This circular movement of hot air and cold air creates a thermal updraft, otherwise know as a convection current.

Thought-Provoking Questions

1. Identify one area in daily life where forced convection plays a useful role?Answer: The furnace in a house that uses a fan to move the air uses forced convection. This furnace is a device that utilizes convection to heat a house. An electric coil inside of the unit heats the intake air to a temperature that exceeds the ambient temperature outside of the unit. An internal fan then blows the hot air through the ducts of the house and into the rooms. 2. Identify one area in daily life where natural convection plays a useful role?Answer: Cooking pasta in boiling water uses natural convection. As the flame of the burner touches the pot (conduction), the hydrogen bonds in the water begin to break apart due to the energy that is being introduced into the water in the from of heat. The hot water rises due to its decrease in density and the buoyant force that is acting upon it. As the water rises away from its heat source it begins to cool, gets denser and sinks. This movement is called a convection cell. When the water boils, it cooks the pasta. 3. Can convection be possible without density or buoyancy? Explain your answer. Answer: No, it is not possible because both are needed and each affects the other. For example density is determined by how tightly packed together the molecules are in an object or substance. If something is very dense (colder), then it will sink. If the object or substance is less dense (hotter) then it will rise or float on the surrounding material. The relationship between an objects ability to float (buoyant force) and its density are directly related.

Applications To Everyday Life

Three instances where convection can be used to explain other phenomenon include: 1. Theory of Plate Tectonics: Sections of the Earth’s crust ride upon a layer called the mantle. The mantle is a layer of molten rock, which surrounds the center of the earth called the core. The core is made up of hot, solid metal and is heated by a radioactive decay. As the mantle rocks heat up and come in contact with the core, they begin to melt into a substance called magma (molten rock). The hotter the magma gets, the less dense it becomes and the higher up it floats (away from the core in all directions). The colder magma sinks and the hotter magma rises. This causes movement in the form of convection cells. These convection currents move the Earth’s plates. 2. Tornados: Changes in temperature in the Earth’s atmosphere contribute to some degree to the formation of extreme weather systems. The correct conditions of convection in the atmosphere, along with certain pressure conditions can result in the formation of tornadoes. 3. Earthquakes: Movements along faults and plate boundaries within the Earth’s crust have been proven to be a direct result of movement in the Earth’s mantle. The movement in the mantle is caused by convection currents.

Think-Pair-ShareConvection Currents

Have you ever wondered….

· how your clothes dryer dries your clothes?

· how your fireplace heats your house?

· how your blow dryer dries your hair?

With your partner, briefly describe the scientific principle that is common in enabling these three items to work:

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Experiment: ”The Tea Bag Rocket”

With your partner, repeat the experiment that you just observed and answer the question below. Be prepared to share your answer with the class.

Describe how this experiment demonstrates natural convection: __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Order of Presentation

NEED TO KNOW :

1. Power point: Have you ever wondered?

2. Scroll through the power point, reading the slides.

3. Pass-out student worksheets for the Think-Pair-Share activity. Have students work in pairs or groups to write a response from the worksheet: “Briefly describe the scientific principle that is common in enabling these three items to work.” (5 minutes)

4. Ask students to share their responses with the class.

SAY… “It sounds like we are talking about a form of heat transfer called Convection that is necessary in the working of items we use every day in our lives. ”

POWER POINT

1. Going back to the power point, scroll through the slides that explain the concept of Convection. Explain the concepts presented.

EXPERIMENT (teacher)

1. Conduct “The Tea Bag Rocket” experiment, showing and explaining what was just discussed in the power point.

EXPERIMENT (students)

1. Pass-out experiment supplies to students. Guide them in repeating the experiment.

2. Ask students to write their responses from the worksheet: “Describe how this experiment demonstrates natural convection.”

EVALUATION:

1. Ask students to share their written responses with the class. Observe the appropriate use of academic vocabulary related to the science concepts presented, as well as the understanding of the scientific principles taught.