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SCIENCE of the PHYSICAL WORLD

Explore the concepts of temperature and thermal energy and learn how they differ from each other. Discover how thermal energy affects temperature and how different substances can have the same temperature but different thermal energy. Understand the three ways heat is transferred - conduction, convection, and radiation. Convert temperature units and learn about the Kelvin scale. Gain knowledge on the transfer of thermal energy in everyday life.

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SCIENCE of the PHYSICAL WORLD

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  1. SCIENCE of the PHYSICAL WORLD “Thermal Energy”

  2. Temperature and Thermal EnergyWhat’s the difference? • Temperature IS NOT HOW HOT OR COLD SOMETHING IS! • Temperature is defined as the measure of the average kinetic energy of the individual particles in an object/substance. • What is kinetic energy? • What does average mean?

  3. Temperature • The higher the average KE, the higher the temperature • Which substance has a lower temperature?

  4. Temperature and Thermal EnergyWhat’s the difference? • Thermal energy is defined as the total energy of all the particles in an object/substance. • What differences do you see in these definitions?

  5. Temperature and Thermal Energy TEMPERATURE IS a measure of the average kinetic energy of the molecules in a substance. Thermal energy is Thermal energy is defined as the total energy of all the particles in a substance Adding thermal energy to a substance increases the average kinetic energy of the molecules and therefore causes a rise in temperature. Higher temperature = faster molecular motion Lower temperature = slower molecular motion

  6. Temperature is not the same as Thermal Energy • Thermal energy is the TOTAL internal energy of the molecules making up a substance • Temperature is the AVERAGE kinetic energy of each of the molecules making up a substance • TE is total; temperature is per molecule

  7. Temperature VS Thermal Energy • You have two containers with water at 90ºC • One container has a mass of 10 g, and the second has a mass of 5 g. ( there’s more substance in one container than another!) • They are at the same temperature, but the 10 gram sample has more thermal energy • TE depends upon mass, but temperature does not.

  8. A THERMOMETER IS AN instrument used for measuring temperature . . . . . . . As the liquid (usually alcohol) in a thermometer gets warmer, it expands and rises in the tube. The opposite happens as the liquid gets cooler.

  9. CELSIUS SCALE is used to measure temperature in the metric system. CELSIUS FAHRENHEIT boiling 100 degrees point212 degrees (water) human 37 degrees body 98.6 degrees temp freezing 0 degrees point32 degrees (water)

  10. SCIENTISTS SOMETIMES USE another metric temperature scale  the KELVIN SCALE. The LOWEST temperature than can be reached ( a point in which all molecular motion stops ), is called ABSOLUTE ZERO or 0 K. (page 438) You can CONVERT Celsius degrees to Kelvins (K) simply by ADDING 273 to the Celsius temperature. 0 ºC = 273 K 100 ºC = 373 K 0 K = -273 ºC

  11. Convert Fahrenheit to Celsius • 1.Determine the temperature in Fahrenheit 2.Using your calculator, subtract 32 3.Multiply the result times 5 4.Divide that answer by 9 5.Your final answer is the temperature in Celsius • Tips: 1. For the math purist, the formula is (F-32)*5/9 = C 2. Is close good enough? No calculator handy? Take Fahrenheit, subtract 30, then divide by 2

  12. Convert Celsius to Fahrenheit • 1.Determine the temperature in Celsius 2.Using your calculator, multiply the temperature times 1.8 3.Add 32 to the result 4.Your final answer is the temperature in Fahrenheit • Tips: 1. For the math purist, the formula is (C*1.8)+32=F 2. Is close good enough? No calculator handy? Take Celsius X 2, then add 30

  13. What is Heat? • Heat is the movement of thermal energy, or the transfer of thermal energy, from one substance to another; • Heat is transferred from warmer to cooler objects. • Heat is transferred in three ways: • Conduction, Convection, and Radiation

  14. CONDUCTION . . . . . . . . . . . . . . . heat transferred through a substance or from one substance to another by direct contact of molecules. CONDUCTION can take place in solids, gases, and liquids, but takes place BEST in solids, because the molecules of a solid are in direct contact with one another. SUBSTANCES THAT DO NOT conduct heat easily are called insulators. Insulator example #1. . . glass

  15. Insulator example #2 . . . . rubber Insulator example #3. . . . plastic

  16. . . . . and insulator #4 . . . . . . . . . wood

  17. CONVECTION . . . . . . . . . . . . . . . . . . . heat energy transferred through liquids and gases by means of up-and-down movements called convection currents. WHEN A LIQUID is heated, the molecules begin to move faster. These convection currents can be observed in a boiling pan of pasta – the rolling of the boiling water is an example of convection currents in a liquid . . . . . . . . as well as a . . . home furnace boiling pasta

  18. Weather patterns and their movement are dependant on convection currents . . . . .

  19. RADIATION . . . . . . . . . . . . . heat energy transferred through space. Heat from the sun reaches the Earth by means of RADIATION . . . . . . ( 8 minutes at 186,000 miles per second). Radiation example #1 . . . . fireplace . . .

  20. Radiation example #2 . . . . heat lamp

  21. Energy from the sun • Thermal energy is transferred from the sun to earth by radiation • Thermal energy is transferred from the air to the ground and other substances that are touching by conduction • Thermal energy is transferred throughout the atmosphere, (and also through the oceans!) globally, by convection

  22. Heat and Chemical EnergyVideo Questions • Differentiate between the Celsius, Fahrenheit and Kelvin Scales for Temperature. • What is Absolute Zero? • Describe the three ways heat is transferred. • Why does winter clothing help you stay warm on a cold day?

  23. Heat and Chemical Energy Video Questions Continued • Why do we say that convection is responsible for Earth’s weather patterns? Explain the process. • Explain how the sun provides heat and chemical energy to people on Earth.

  24. Quick Quiz – 10 minutes • Name three ways that heat energy is transferred within a substance or from one substance to another. • Which type of heat transfer is responsible for our weather? • Heat energy moves from ______ substances to _______ substances. • You have two glasses, one with 50 ml and one with 100 ml. They both have a temperature of 70 degrees Celsius. Which has more heat energy? Why? • Bonus: What is Absolute Zero?

  25. Measuring Heat . . . . . . . HEAT CANNOT BE MEASURED directly, but changes in temperature CAN BE measured directly, thus providing a way to measure heat indirectly. HEAT IS MEASURED in units called CALORIES. One calorie is defined as the amount of heat needed to raise the temperature of 1 gram of water 1 degree Celsius. (1 calorie = 4.19 Joules) Notice what measurements are involved: Temperature, heat energy, and mass For water, to raise one gram from 3ºC to 4 ºC, you need to add one calorie of heat energy; Two calories would raise it 2º C

  26. The Calorie • The calorie is a small unit used to measure energy • Food labels use Calories • 1 Calorie is a kilocalorie • 1 Calorie = 1000 calories

  27. Heat and Phase Changes THE PHYSICAL CHANGE of matter from the solid phase to the liquid phase is called PHASE CHANGE. PHASE CHANGES REQUIRE a change in heat energy. PHASE CHANGES: FREEZING POINTS  (0 degrees C or 32 degrees F purewater ) The temperature at which a substance changes from the liquid phase to the solid phase.(page 452)

  28. MELTING POINT  the temperature at which a substance changes from the solid phase to the liquid phase. (page 451) BOILING POINT  (100 C or 212 F pure water ) The temperature at which a substance changes from the liquid phase to the gas phase. (page 452)

  29. DURING A phase change: 1. There is a change in heat energy. 2. There is no change in temperature. ONLY AFTER A PHASE change is complete will a change in heat energy . . . . result in a change in temperature. THERMAL EXPANSION is the increase in size of a substance caused by heat; (this is due to the increase in molecular motion). Solids, liquids, and gasses all expand when temperature is increased.

  30. SOLIDS . . . . . . . The kinetic energy of the molecules increases the speed of their vibrations resulting in an increase in distance between the molecules, (this accounts for the expansion of solids).(page 450)

  31. LIQUIDS . . . . . . . Most liquids expand when they are heated. Exception: water expands as it cools. As the volume increases, the density decreases.

  32. THERMAL EXPANSION is useful in heat-regulating devices such as the . . . . . . . . . . . . . THERMOSTAT, (used to control air temperature in buildings). (page 454) . . . and finally . . . .

  33. GASES . . . . . . As the temperature increases the molecules move faster and faster and the results can be quite dramatic . . . . . . . . . . . perhaps an explosion!

  34. What about mass? • A calorie raises ONE gram, one degree? What if we wanted to raise 10 grams one degree? • It would take one calorie for each gram, or 10 calories! • Not only does mass affect heat energy, but so does the type of substance. Remember, some substances transfer heat better than others!

  35. Specific Heat The ability of a substance to absorb heat energy is called its SPECIFIC HEAT, A substance’s Specific Heat is the number of calories needed to raise the temperature of 1 gram of a substance 1 degree Celsius. THE SPECIFIC HEAT of water is 1 calorie per gram per degree Celsius or (1.00cal/g degrees C). (page 444)

  36. Calculating Specific Heat SPECIFIC HEAT CAN BE used to calculate the amount of heat gained or lost by a substance. HEAT GAINED (or lost) = Mass X Change in Temperature X Specific Heat ΔQ = m x ΔT x C

  37. Calculating Specific Heat • How much energy is needed to raise 500 g of water 10º C ? ΔQ = m x ΔT x C ΔQ = 500g x 10º x 1 cal/g ºC ΔQ = 5000 calories

  38. Different materials have different specific heat values • Aluminum has a specific heat of 0.22 cal/gºC • What if we had 500 g of aluminum, and wanted to raise it 10ºC? ΔQ = m x ΔT x C ΔQ = 500g x 10º x 0.22 cal/g ºC ΔQ = 1100 calories It takes only 1100 calories for aluminum, but 5000 calories for Water! Which is the better conductor?

  39. Specific Heat Problems • Calculate the heat lost by 10 grams of Copper cooled from 35ºC to 21ºC. C = 0.09 cal/gºC ΔQ = m x ΔT x C ΔQ = 10 x 14 x 0.09 ΔQ = 12.6 calories • 10 grams of a certain substance gained 16.5 calories of heat when the temperature went from 70ºC to 85ºC. What is the specific heat of the substance? ΔQ = m x ΔT x C 16.5 = 10 x 15 x C 16.5 = 150C 0.11 cal/gºC = C

  40. Specific Heat of some other substances

  41. WHEN HEAT ENERGY IS stored, (potential energy), there is no change in the temperature of a substance. POTENTIAL HEAT ENERGY is present in chemical substances such as gasoline and other fuel . . . The stored energy is released when the fuels are burned . . . . .

  42. FOODS ALSO contain potential heat energy when released during the process of respiration. The amount of heat a food gives off is indicated by the number of calories it contains.

  43. End of Class Notes !!!

  44. REVIEW QUESTIONS L-A NOTE THAT full credit will be given only for those answers, which are COMPLETE, ACCURATE and THOROUGH. A 1. Why is the air pressure in a car’s tires different before and after the car has been driven for several hours? 2. Explain why a temperature of –273oC is called absolute zero. 3. Write out the questions and answer completely “Section 1 Review”,#1 5, page 438 in your science textbook.

  45. B LA • What is the relationship among work, heat, and energy? • 2. Compare the three methods of heat transfer in terms of how heat moves and the types of substances in which the transfer takes place. • Refer to the drawing of the baseboard heating • system in Figure 6 in you science textbook (page 441). Sketch, label, and describe the components of this convection heating system.

  46. C LA • How can the human body’s use of food be compared to a heat engine? • Why will the particles of a gas at room temperature be spread throughout a room? • 3. Explain how heat affects matter during a phase • change. • 4. Why does placing a jar under warm running • water help loosen the lid on the jar? • In a hot-air balloon, air heated by a flame. • 5. Explain how this enables the balloon to float in the air.

  47. D LA • What is the difference between heat and temperature? • Describe how a thermostat controls the temperature in a house. • Why does an ice cube float in water instead of sinking to the bottom of the glass? • What is the significance of bubbles forming in a liquid that is being heated? • 5. How does a thermometer make use of the property of thermal expansion?

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