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Convection

Convection. Focus Question: How does convection transfer energy through fluids (liquids, gas)?. Objectives. I can explain density as well as calculate the density of a material using an equation. I can explain what mass means. I can explain what volume means.

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Convection

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  1. Convection Focus Question: How does convection transfer energy through fluids (liquids, gas)?

  2. Objectives • I can explain density as well as calculate the density of a material using an equation. • I can explain what mass means. • I can explain what volume means. • I can explain how convection works. • I can describe how materials of different densities interact.

  3. Heat in Solids and Liquids • In solids, atoms and molecules are pretty much locked into positions in relationship to one another. When radiant energy is absorbed by one area in a solid, the molecules begin to vibrate more. The vibration and the motion spreads. • That’s how heat is conducted through a solid material-by vibrational energy, one molecule to the next.

  4. Heat in Solids and Liquids • In fluids (both liquids and gases) molecules are not locked into position. They can move toward, away from, and past one another. Heat can transfer from one place to another in a liquid or gas by conduction – molecules hitting one another – and by absorption of radiant energy. • There is another way, however, that energy moves in fluids. That’s what we will try to observe today.

  5. Challenge of the day • There are four liquids • Layer all four liquids in a section of straw

  6. Materials Container with 4 liquids Pipettes (4) Paper Towels Straw & holder

  7. Using the straw • Push straw over ball of holder at a slight angle.

  8. Gently squeeze a few drops of each liquid into the straw. • Let the drops slide down the side of the straw.

  9. Directions • Record all trials using colored pencils on the “Liquid Layers” worksheet. • Circle the correct layering diagram. • Answer the question for Part 2.

  10. Discussion What do you think caused the salt solutions to layer this way?

  11. Discussion • The liquids are made with water and salt. • How is it that some salt solutions can be heavy and some light if they are made with the same materials?

  12. Ponder this! Which is heavier? Gold or Feathers

  13. Mass vs. Volume(Add definitions to Notebook.) Mass • The amount of molecules in an object • You find mass by measuring the weight Volume Is how much space a sample of matter occupies - measuredusing graduated cylinders

  14. Density • The amount of matter in a volume of material • Density = mass / volume • Ratio between the mass of matter and its volume • Equal volumes of material • One is heavier than the other • Heavier material is denser

  15. Determining Density Will these 2 identical volumes of liquids have the same mass? Make a prediction!

  16. Masses of cups Mass 25.0 g Mass 28.2 g Which solution is denser? How do you know?

  17. Discuss with group • Which solution would layer on top of the other? • What does this tell you about how liquids of different densities interact? (Which one will be on top?)

  18. What does this tell you about how liquids of different densities interact? (Which one will be on top?) • On the “Liquid Layers”, • write the masses and volumes.

  19. Densities of colored salt solutionsDensities of colored salt solutions • Turn to “Calculating Density”. • Transfer data from the “Liquid Layers” page. • Calculate the density (D = M / V) and answer the questions at the bottom. • See next slide for examples.

  20. Calculating Density • Sample 1: • M(g)/V(cc or mL)= Density • 54g/45cc = • Sample 2: • 132g/120cc =

  21. Answer • Red = 1.00 g/ml • Green = 1.06 g/ml • Yellow = 1.13 g/ml • Blue = 1.20 g/ml

  22. Discuss Density • The red solution was pure water with red coloring. What is the density of water? • Which solution was densest? How do you know? • What is the relationship between layering and density? • What happens when you try to layer a denser solution on top of a less dense solution?

  23. Pine wood has a density of 0.60 g/cc. Will it float or sink in water? • Styrene plastic has a density of 1.7 g/cc. Will it float or sink in the red saltwater solution? • What general statement can you make about floating and sinking in water?

  24. Density Review(Add this to your Notebook.) • Density can be calculated if you know volume and mass. • Volume can be measured in milliliters (mL) or cubic centimeters (cc). • Mass can be determined by weighing. • Density is mass per volume (mass/volume). • Always include the units with your calculations and answers.

  25. Response Sheet • Turn to Lab page 25. • Answer the question and turn in your worksheet.

  26. Reading • Read “Density” on page 27 of the Green Resource Book. • Answer questions.

  27. Layers of Water • Today we have a challenge: Make layers with plain water of different temperatures. • Wait for me to pass out a piece of paper!

  28. Layers of Water Materials 3 Vials (2 with caps) HotWater, ColdWater, Regular Water 2 Foam cups 2 Pipettes 1 Plastic cup

  29. Some useful tips • Use the clear plastic cup to dump out failures. • Put a piece of white paper behind your vials. (it helps show the layers easier)

  30. Success! • After you successfully layer the vial of water, leave the vial alone and observe it for five minutes. • Discuss with the students at your table what happens.

  31. Observations • What happened in your vial after it sat alone for a few minutes? (#4 on your worksheet) • What do you think caused the redwater to start to descend (go down)?

  32. Density • Different solutions contain different amount of mass. The same volume of water can contain different amounts of mass making one heavier or more dense than another. • If our two solutions have different densities, which one layers on top?

  33. Density • Let’s discuss why the red and blue liquids went to where they went.

  34. Back to the worksheet • Complete #2 and #3 on your worksheet.

  35. Need more heat • Let’s see what happens when a layered vial is placed in a couple centimeters of hotwater. Work with your group: (#5 on worksheet) Create another three-layer vial I will pour about 1 cm of hotwater in your plastic cup Place the layered vial carefully in the cup of hot water and observe Be ready to share your observations

  36. Molecules and Water Density • As heat is absorbed by water, the molecules move faster and bang into each other more and more. This makes the molecules become farther apart thus making the water less dense.

  37. Convection • When a mass of fluid is warmer or colder than the surrounding fluid, the mass will rise or sink in the surrounding fluid. • This motion of masses because of difference in density resulting from temperature, is convection. Convection is the third way heat moves from one place to another. • Convection happens only in fluids, where molecules are free to flow. jewelsltc@yahoo.com

  38. READING Convection Pg. 32

  39. Word Bank • Density – the amount of mass in the volume of a substance • Convection - motion of masses of fluid because of the change of density from temperature change

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