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T hermal E nergy

T hermal E nergy. History of Thermal Energy. Heraclitus, Greek: earth, fire, water Bacon 1200’s: motion produced heat Bernoulli 1700: fluids flow and are made of invisible particles Joseph Black: heat is an invisible fluid. Caloric Theory.

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T hermal E nergy

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  1. Thermal Energy

  2. History of Thermal Energy • Heraclitus, Greek: earth, fire, water • Bacon 1200’s: motion produced heat • Bernoulli 1700: fluids flow and are made of invisible particles • Joseph Black: heat is an invisible fluid

  3. Caloric Theory • Scientists used to think thermal energy was an invisible fluid that flowed from hot objects to colder ones. • They called this fluid caloric. • It was made of self-repelling particles • Temperature measured caloric flow

  4. Caloric Theory • Lavoisier considered caloric to be an actual fluid. • Hot objects had a lot of caloric. • Caloric naturally flows from hot objects to cold ones. • Temperature was a measure of the density of caloric.

  5. Advantages of Caloric theory • Explained gas laws • Basis for scientific development of steam engine • Explained why gases expand • Explained the speed of sound in air

  6. Benjamin Thompson • He was a scientist better known as Count Rumford, who disproved the caloric theory. • He did this by observing the boring of cannon barrels.

  7. Benjamin Thompson • He noticed that dull bits produced little cutting but much heat, while sharp bits produced much cutting and less heat. • This would mean that the amount of caloric in the same metal could change, which is impossible.

  8. James Prescott Joule • He was the first to understand the connection between mechanical energy (motion) and heat.

  9. James Prescott Joule • If heat is not a fluid, what is it? • Heat is caused by motion. • The Greek word for motion is kinetos, from which we get “kinetic.”

  10. Kinetic-Molecular Model • When Kelvin calculated the speed of molecules in air based on their kinetic energies, this firmly established this model. • Thermal energy is the total of all the kinetic energy of all the particles in an object.

  11. Kinetic-Molecular Model • Are there any other energies in the particles of an object? • Yes. There are attractions and repulsions between the particles.

  12. Kinetic-Molecular Model • The sum of all these energies is called the internal energy of the substance. • This energy cannot be measured, but the thermal energy can be measured.

  13. warmer system cooler system Kinetic-Molecular Model • The transfer of kinetic energy from one substance to another is called heating or cooling.

  14. Who developed the caloric theory? • Count Rumford • Benjamin Franklin • Benjamin Thompson • Lavoisier

  15. According to the caloric theory, heat is a _____. • solid • gas • fluid • movement of matter

  16. According to the kinetic theory, heat is a _____. • solid • gas • fluid • movement of matter

  17. Temperature

  18. How Do We Measure Hot and Cold? • What is hot to one person is not necessarily hot to someone else. • Scientists need to measure “hotness.” • They use temperature which is measured in units called degrees.

  19. Temperature • Temperature is a measure of the AVERAGE kinetic energy (motion) of the particles. • As the particles speed up, they move up the thermometer.

  20. Thermometers • Thermometers work by utilizing the thermometric property that fluids expand when heated. • This expansion forces the fluid up the thermometer.

  21. Thermometers • Galileo made an early thermometer around 1600, but it was open at one end and was affected by air pressure. • Most thermometers contain either alcohol or mercury.

  22. Thermometers thermometric medium expands heating of thermometer bulb

  23. Temperature Scales • Temperature scales must be calibrated by using fixed, easily reproducible temperatures as a standard. • These standards are called fiducial points. • There are 3 temperature scales that will be covered.

  24. Fahrenheit • Daniel Gabriel Fahrenheit invented the mercury thermometer and the Fahrenheit temperature scale.

  25. Fahrenheit • This is the temperature scale used in the United States. • Fahrenheit used 0° as the coldest temperature he could make using an ice, salt, and water mixture. • His other fiducial point was the blood of a healthy man.

  26. Fahrenheit • Fahrenheit later changed the fiducial points to the freezing and boiling points of water, 32° and 212° respectively, for a difference of 180°.

  27. Celsius • He was a Swedish astronomer who created the Celsius temperature scale. • He used the same fiducial points but only had 100 degrees difference. • Surprisingly he chose 0° as the boiling point and 100° as the freezing point!

  28. Celsius • Because there are fewer degrees between the freezing and boiling in Celsius than in Fahrenheit, a Celsius degree is larger.

  29. Converting Between C and F Method 1 • tc = 5/9 (tf + 40°) − 40° • tf = 9/5 (tc + 40°) − 40°

  30. Converting Between C and F Method 2 • C = 5/9 (F − 32°) • F = 9/5 C + 32°

  31. Sample Problem 1 Method 1 Change 100 °F to °C. tc = 5/9 (tf + 40°) − 40° = 5/9 (100 °F + 40°) − 40° = 5/9 (140°) − 40° = 77.7 − 40° = 37.8 °C −

  32. Sample Problem 1 Method 2 Change 100 °F to °C. C = 5/9 (F − 32°) = 5/9 (100 °F − 32°) = 5/9 (68°) = 37.8 °C

  33. Sample Problem 2 • Method 1 Change 75 °C to °F. tf = 9/5 (tc + 40°) − 40° = 9/5 (75 °C + 40°) − 40° = 9/5 (115°) − 40° = 207 − 40° = 167 °F

  34. Sample Problem 2 Method 2 Change 75 °C to °F. F = 9/5 C + 32° = 9/5 • 75 °C + 32° = 135 + 32° = 167 °F

  35. Temperature measures _______. • average kinetic energy • total kinetic energy • heat • cold

  36. Change 32 °C to °F. • 100 °F • 90 °F • 58 °F • 0 °F

  37. Change 32 °C to °F. F = 9/5 C + 32° = 9/5 • 32 °C + 32° = 57.6 + 32° = 89.6 °F

  38. Change 325 °F to °C. • 527 °C • 149 °C • 163 °C • 617 °C

  39. Change 325 °F to °C. C = 5/9 (F − 32°) = 5/9 (325 °F − 32°) = 5/9 (293°) = 163 °C

  40. Kelvin • Lord Kelvin was a British physicist who did extensive work in the fields of electricity and thermodynamics. • He created the Kelvin temperature scale.

  41. Kelvin • He realized that all gases occupy less volume as they are cooled. • He calculated that the volume of a gas would decrease to 0 at about -273 °C.

  42. Absolute Zero • This is the temperature at which kinetic energy is at a minimum. • It equals 0 K, which is -273 °C, which is -459.4 °F. • That is COLD!!!

  43. Kelvin • He could not use this as a fiducial point since it cannot be achieved according to the law of thermodynamics. • Instead, he used the triple point of water as the fiducial point.

  44. Kelvin • The triple point is the temperature and pressure at which solid, liquid, and gaseous phases of the substance simultaneously exist in a stable condition.

  45. Converting between C and K • K = C + 273 • C = K − 273

  46. Sample Problem 3 Change 300 K to °C. C = K − 273 = 300 K − 273 = 27 °C

  47. Sample Problem 4 Change -35 °C to K. K = C + 273 = -35 °C + 273 = 238 K

  48. Sample Problem 5 Change 124 K to °C. C = K − 273 = 124 K − 273 = -149 °C

  49. Sample Problem 6 Change 678 °C to K. K = C + 273 = 678 °C + 273 = 951 K

  50. Converting between F and K • In order to change from °F to K or vice-versa, first change to °C and then to the desired scale.

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