Bell Ringer

1. Bell Ringer Name: 3/10/2009 What date is the Brewers home opener? Response

2. New Seating Chart • Find your new seat for the grading period

3. Change to late assignment policy • Everything is now going to be posted to the web • Lectures • Labs & solutions • Homework assignments & solutions • Tests and quizzes & solutions • Once a solution is posted, the lab or homework will no longer be accepted • The exception is for excused absences

4. Labs • Labs are not recess for middle schoolers

5. Extra Credit • Need one volunteer from each class to learn enough about the smartboard software to demonstrate how to draw using it. • This will be for our next concept map lesson

6. Heat of Fusion Lab Review • Each student started with 10 • -1, if the hypothesis was blank • -1, if the predicted final temperature had incorrect units or was outside a reasonable range • -1, if there was no mass for the Styrofoam cup • -1, if there was no readings for mass of the water • -1/2, if there was a mass reading for the water but I couldn’t tell if it included the cup or not

7. Heat of Fusion Lab Review • -1, if there was no initial temperature reading • -1, if there was no mass reading for the ice • -1/2, if there was a mass reading for the ice but I couldn’t tell if it included the cup or not • -1, if there was no reading for the final temperature • The second page was graded as extra credit • +1/4, if #1 indicated the heat was absorbed by the ice

8. Heat of Fusion Lab Review • +1/2, if #1 indicated the heat was absorbed by the ice then transferred to the surroundings • +1/4, if #2 had the proper values substituted into the formula • +1/4, if #3 showed the Q from #2 was divided by the proper ice mass • +1/4, if #4 had all proper values substituted into the formula • +1/4, if #5 indicated that was much greater than c • +1/4, if #6 used the value from #4 or #3 to compute an error

9. Heat of Fusion Lab Review

10. Heat of Fusion Lab Review

11. Heat of Fusion Lab Review • Calculating total energy for process • Energy gained by ice = Energy lost by water

12. Chapter 23 Homework Extra credit: Use for the phase change and for the change as water, then add them together. at phase change after phase change

13. Thermodynamics • Thermodynamics - the study of heat movement • Thermodynamics concentrates on the macroscopic (big) world, rather than the microscopic (tiny) world • Thermodynamics provides us with theories for operating heat engines

14. Absolute Zero • No upper limit on how quickly molecules can move because of kinetic energy • There is a definite lower limit called absolute zero. The kinetic energy approaches zero.

15. Absolute Zero • Which is larger, a Celsius degree or a Kelvin degree?

16. Absolute Zero • Which is larger, a Celsius degree or a Kelvin degree? • Neither, they are both the same.

17. Absolute Zero

18. Thermodynamics History • In the 17th century heat was thought to be an invisible fluid called caloric • Caloric flowed from hot to cold objects • Caloric was conserved in its interactions

19. Thermodynamics History • If objects only get warm because of heat transferred from another object, how do my hands get warm if I rub them together?

20. Thermodynamics History • If objects only get warm because of heat transferred from another object, how do my hands get warm if I rub them together? • something you learned about a while back, friction • recall that work = force * distance • and friction is a force acting over a distance

21. Thermodynamics History • Metal workers noticed heat transfer while drilling cannons a long time ago. • It took a while for anyone to realize that friction from the drill bits was making the cannon barrels hot.

22. Thermodynamics History • In the 1840’s it became understood that the flow of heat was nothing more than the flow of energy and caloric theory was abandoned • James Joule used the paddle-wheel apparatus to compare heat energy with mechanical energy

23. Thermodynamics History James Joule tried to measure the expected increase of water moving over a waterfall and landing in the pool below. His measurements did not confirm his estimates, so he developed the paddle-wheel apparatus to use instead

24. Thermodynamics History • Today heat is viewed as a form of energy which can neither be created nor destroyed

25. First Law of Thermodynamics Whenever heat is added to a system, it transforms to an equal amount of some other form of energy

26. First Law of Thermodynamics • What happens when you strike a penny with a hammer, besides it getting dented and flatter?

27. First Law of Thermodynamics • What happens when you strike a penny with a hammer, besides it getting dented and flatter? • It gets hot • Energy is converted from potential to thermal in form

28. First Law of Thermodynamics • Back to rubbing our hands together. What is the effect of the work done?

29. First Law of Thermodynamics • Back to rubbing our hands together. What is the effect of the work done? • Our hands get warm • Work is converted from potential to thermal in form • Can thermal energy be easily converted into work?

30. First Law of Thermodynamics • Our book restates the first law of thermodynamics as: Heat added = increase in + external work internal energy

31. First Law of Thermodynamics • If a hollow object is heated on a stove, and it doesn’t move, then the heat is transferred to the inside to the object increasing its kinetic energy • But if the object can perform mechanical work, then the internal kinetic energy would be lessened • An example of this would be a piston in a steam engine

32. First Law of Thermodynamics • In a steam engine, the piston is forced to move because the steam pushes on the piston as it expands • The piston moves and work is performed • The energy transferred to the piston will be reduced by the amount of work done Heat added = increase in + external work internal energy

33. First Law of Thermodynamics • Can the process move in the other direction, that is, work adding heat into the process?

34. First Law of Thermodynamics • Can the process move in the other direction, that is, work adding heat into the process? • Yes, think of a mechanical tire pump being used to inflate a tire • It gets hot

35. Adiabatic Processes • Compression or expansion of a gas, when no heat enters or leaves is said to be adiabatic. • Adiabatic changes occur so rapidly that the heat has little time to enter or leave. • The best example is the cylinders in an automobile engine.

36. Adiabatic Processes • In the automobile engine, the gases in the piston chamber expand and contract so quickly that most of the heat stays in the chamber • We have a repeating cycle of: • Work being done on the gas by compressing it • Gas gaining internal energy and warming • The gas expanding and performing work • The gas then gives up energy and cools

37. Adiabatic Processes • A while back we talked about blowing air on your hand with your mouth wide open • Its warm • If you narrow your mouth opening and blow air again • Its cooler • Adiabatic expansion is occurring and causing the cooling

38. Adiabatic Processes • Many weather changes are driven by adiabatic processes where: • Change in air temp ~ Change in air pressure • It requires large masses of air for the effect to be adiabatic • The changes occur around the edges of the masses • Chinook winds are an example where cold air moves down slope, compresses and warms

39. Adiabatic Processes • Why does air moving quickly down the mountainside feel warm?

40. Adiabatic Processes • Why does air moving quickly down the mountainside feel warm? • Cold air moves down slope, compresses and then warms • Chinook winds are an example where

41. Second Law of Thermodynamics Heat will never of itself flow from a cold object to a warm object.

42. Second Law of Thermodynamics • We’ve been talking about this for a couple weeks now and seen many examples. • We’ve only seen energy transfer from a warm object to a cold one

43. Second Law of Thermodynamics • The heat pump is an example of energy flowing in the other direction, but work is required to accomplish the task.

44. Heat Engines • Work can be changed completely into heat • Rub your hands together • Changing heat completely into work can never occur • The best we can do is convert some heat into mechanical energy

45. Heat Engines • The heat engine is any device that converts internal energy into mechanical work • Steam engine • Automobile engine • Jet engine • The mechanical work can only be obtained when heat flows from high temperature to low temperature

46. Heat Engines • When heat engines are discussed, reservoirs of high and low temperature are frequently mentioned • Heat absorbed from high temperature reservoir • Some converted into mechanical work • Remaining heat expelled to low temperature reservoir

47. Heat Engines • In the gasoline engine: • Fuel burned in the high temperature reservoir or combustion chamber • Mechanical work is done on the pistons • Remaining heat expelled as exhaust fumes

48. Heat Engines • Before the 2nd law was understood, it was thought that low friction devices might convert nearly all energy to useful work. • In 1824, Sadi Carnot analyzed the cycles of compression and expansion and discovered that the heat converted to useful work depends on the temperature difference between the high and low temperature reservoirs.

49. Heat Engines • The relationship is summarized by the following equation: • when all temperatures are measured in Kelvins

50. Disorder • The 1st law of thermodynamics states that energy can’t be created or destroyed • The 2nd law of thermodynamics adds that whenever energy transforms, some of it degenerates into waste • The waste energy is unavailable and lost