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The Sun’s Energy Heat Transfer Unit

The Sun’s Energy Heat Transfer Unit. NSTA Web Seminar Energy: first 9 slides adapted for 8 th grade from. Bill Robertson. Energy is neither created or destroyed but it changes form. In other words, energy may be converted from one form to another, but it doesn't just disappear or increase.

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The Sun’s Energy Heat Transfer Unit

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  1. The Sun’s Energy Heat Transfer Unit

  2. NSTA Web SeminarEnergy: first 9 slides adapted for 8th grade from Bill Robertson Energy is neither created or destroyed but it changes form. In other words, energy may be converted from one form to another, but it doesn't just disappear or increase.

  3. Heat is… • Energy given off or absorbed by an object • How fast the molecules in an object are moving. • The total amount of molecular energy in an object Temperature is the measure of….. • The total amount of energy in an object • How fast the molecules in an object are moving

  4. We use a thermometer to measure temperature, but how does the thermometer know how hot the substance is?

  5. The molecules of the substance bump into the thermometer and transfer energy. How often and how hard they bump into the thermometer are directly related to their speed. Temperature turns out to be related to the average speed of the molecules in a substance.

  6. Thermal Energy: measure of total internal energy • kinetic energy: Energy of motion – doing work. • potential energy: Stored energy in an object – waiting to do work. • What is the difference between a hot cup of coffee and a cold cup of coffee at the molecular level?

  7. 50 degrees C 20 degrees C Heat always transfer from an area of high temperature to low temperature.

  8. 50 degrees C 20 degrees C Heat

  9. Heat transfer • If you touch a hot stove describe the heat transfer. • If you touch an ice cube, describe the heat transfer. • You spoon out a scoop of ice cream. Describe the transfer with the ice cream and the spoon.

  10. Cold Cold is the lack of heat. If you were to touch your tongue to a frozen pole, would cold travel to your tongue?

  11. Temperature Conversions • There are three commonly used temperature scales, Fahrenheit, Celsius and Kelvin.

  12. Temperature Conversions • Converting Between the Kelvin and Celsius Scales • Note that • The temperature unit is the same size. • The zero points are different. • To convert from Celsius to Kelvin we need to adjust for the difference in zero points.

  13. Temperature Conversions • Converting Between the Kelvin and Celsius Scales 70. oC = ? K TC + 273 = TK 70. + 273 = 343 K

  14. Temperature Conversions • Converting Between the Fahrenheit and Celsius Scales

  15. Conduction is the transfer of heat between objects in direct contact with each other. From warmer to cooler

  16. ConductionSolids are better conductors than liquids or gases.

  17. Conduction The transfer of heat through direct contact. Heat flows from the warmer object into the cooler object until they reach equilibrium. The sea of electrons gain kinetic energy and transfer it through the solid. A nail is heated over a burner…..the heat travels along the length of the nail, and if you do not have a heat mit on, Ouch.

  18. You get out of bed the tile floor feels colder than the wooden floor even though they are the same temperature. Why?

  19. Wood is not a good conductor of heat. The tile conducts heat well. So heat is easily conducted out of your foot touching the tile floor. Insulators are not good conductors of heat, that is why you use them in your home – to keep the heat from being transferred to the outside.

  20. Try to explain why firewalkers don’t get third degree burns when walking on wood coals.

  21. What if there were nails in the wood? Don’t try this at home!

  22. Radiation: Electromagnetic waves travel through space. When contacting an object, heat is transferred to the object. HEAT TRANSFER THROUGH SPACE

  23. Radiation – does not require a physical medium to travel.

  24. Dull metal Shiny black Shiny metal Dull black Emission experiment Four containers were filled with warm water. Which container would have the warmest water after ten minutes? The __________ container would be the warmest after ten minutes because its shiny surface reflects heat _______ back into the container so less is lost. The ________ container would be the coolest because it is the best at _______ heat radiation. shiny metal radiation dull black emitting

  25. Dull metal Shiny black Shiny metal Dull black Absorption experiment Four containers were placed equidistant from a heater. Which container would have the warmest water after ten minutes? dull black The __________ container would be the warmest after ten minutes because its surface absorbs heat _______ the best. The _________ container would be the coolest because it is the poorest at __________ heat radiation. radiation shiny metal absorbing

  26. Radiation questions Why are houses painted white in hot countries? White reflects heat radiation and keeps the house cooler. Why are shiny foil blankets wrapped around marathon runners at the end of a race? The shiny metal reflects the heat radiation from the runner back in, this stops the runner getting cold.

  27. Convection is the up and down movement of gasses or liquids caused by heat transfer. This is the primary method that heat moves through gasses and liquids. It is the transfer of thermal energy through currents. As liquids and gases gain energy, they expand and decrease in density, so hot fluids/gases rise and cool fluids sink.

  28. Convection • Warmer areas rise and cooler areas sink. This movement creates a current.

  29. Can you relate Convection to the current of air - wind. Along the shore, the ground warms up more than the water. As the air is warmed, it becomes less dense and rises as more cool dense air settles.

  30. Specific Heat capacity The quantity of heat required to change the temperature of a unit mass of the substance by 1 degree. It is a measure of thermal inertia (resistance to a change in temperature) Water has a much higher specific heat capacity than most other substances. It requires a lot of heat to change temperature. It also takes a long time to cool.

  31. Hot water, just like hot air, rises. Then the cold water rushes in to fill the void. This creates a convection cell.

  32. Convection questions Why does hot air rise and cold air sink? Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air. Why are boilers placed beneath hot water tanks in people’s homes? Hot water rises. So when the boiler heats the water, and the hot water rises, the water tank is filled with hot water.

  33. The heat balance of the Earth http://www.youtube.com/watch?v=wz6wzOtv6rs

  34. The heat balance of the Earth

  35. 1. Which of the following is not a method of heat transfer? A. Radiation B. Insulation C. Conduction D. Convection

  36. 2. In which of the following are the particles closest together? A. Solid B. Liquid C. Gas D. Fluid

  37. 3. How does heat energy reach the Earth from the Sun? A. Radiation B. Conduction C. Convection D. Insulation

  38. 4. Which is the best surface for reflecting heat radiation? A. Shiny white B. Dull white C. Shiny black D. Dull black

  39. 5. Which is the best surface for absorbing heat radiation? A. Shiny white B. Dull white C. Shiny black D. Dull black

  40. Compressed air will heat as it is compressed. As it expands it will cool. With your mouth open, blow on your hand: How does it feel? Now pucker up and make your mouth opening small. How does it feel? Can you explain this?

  41. True or false • A blanket is a source of heat energy!

  42. The heat balance of the Earth

  43. The heat balance of the Earth

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