Understanding Heat: Limits, Kinetic Theory & Laws of Thermodynamics

1. Heat Chapter 6 Notes

2. Heat Can objects get colder and colder or hotter and hotter forever or is there a limit? Why does a tile floor feel colder than carpet at the same temperature? Why does ice form at the top of a pond instead of the bottom?

3. The Kinetic Theory of Matter Matter is made up of tiny particles (atoms or molecules) that are always moving.

4. The Kinetic Theory of Matter The thermal energy of an object is the total energy in the object due to the motion of its particles.

5. Temperature When you strike a nail with a hammer, it becomes warm. Why?

6. Temperature The hammer's blow makes the nail's atoms move faster.

7. Temperature When you put a flame to a liquid, the liquid becomes warmer. Why?

8. Temperature The liquid becomes warmer as its molecules move faster.

9. Temperature In general, the warmer an object, the more kinetic energy its atoms and molecules possess.

10. Temperature Temperature, the degree of hotness or coldness of an object, is proportional to the kinetic energy of the atoms making up the object.

11. Temperature There are two basic scales used to measure degrees of temperature: Fahrenheit (F) and Celsius (C) In science, we will typically use degrees Celsius (C)

12. Temperature There is no upper limit to temperature-theoretically, one can have temperatures as high as many millions of degrees Celsius.

13. Temperature The lowest possible temperature that exists is the temperature at which all kinetic energy of atoms stops. We call this temperature absolute zero, and it is about -273 degrees C.

14. What is heat? If you touch a hot stove, thermal energy from the stove passes from the stove into your hand because the stove is warmer than your hand.

15. What is heat? • If you touch ice, thermal energy from your hand passes to the ice because your hand is warmer than the ice.

16. What is heat? • Heat is the flow of thermal energy due to a temperature difference. • Cold objects are cold because they lack thermal energy.

17. What is heat? • Heat is a form of energy, and is measured in Joules (J) • One unit of heat commonly used is the calorie.

18. What is heat? • A calorie is the amount of heat needed to change the temperature of 1 gram of water by 1 degree C. • 1 calorie= 4.18 J

19. What is heat? • The heat unit for labeling food is the kilocalorie, usually called the Calorie. • 1 Calorie=1000 calories

20. The Laws of Thermodynamics • Thermodynamics= movement of heat

21. The Laws of Thermodynamics • There are 3 laws of thermodynamics:

22. The Laws of Thermodynamics • First Law of Thermodynamics: • Whenever heat flows into and out of a system, the gain or loss of thermal energy equals the amount of heat transferred.

23. The Laws of Thermodynamics • Second Law of Thermodynamics: • Heat never spontaneously flows from a lower-temperature substance to a higher-temperature substance.

24. The Laws of Thermodynamics • Third Law of Thermodynamics: • No system can ever reach absolute zero.

25. Specific Heat Capacity • Have you ever noticed that the filling of hot apple pie can burn your tongue, while the crust does not?

26. Specific Heat Capacity • Or that you can eat toast a few seconds after it comes out of the toaster, while soup takes much longer to cool down?

27. Specific Heat Capacity • Different substances have different capacities for storing thermal energy

28. Specific Heat Capacity • A pot of water might require 15 minutes to boil, while the same quantity of iron or silver would reach that temperature in much less time.

29. Specific Heat Capacity • Water absorbs more heat than iron or silver for the same change in temperature. • We say that water has a higher specific heat capacity.

30. Specific Heat Capacity • Specific heat capacity is defined as the quantity of heat required to change the temperature of a unit mass of the substance by 1 degree Celsius.

31. Heat Transfer: Conduction • Heat can be transferred from object to object in 3 ways: conduction, convection, and radiation.

32. Heat Transfer: Conduction • When you hold one end of a nail in a flame, it quickly becomes too hot to hold. • This method of heat transfer is called conduction.

33. Heat Transfer: Conduction • Conduction occurs by the movement of atomic particles colliding inside a heated object or material and transferring heat.

34. Heat Transfer: Conduction • Good conductors of heat: metals such as silver, copper, aluminum, iron.

35. Heat Transfer: Conduction • Poor conductors of heat: Wood, air, porous substances.

36. Heat Transfer: Convection • Convection is heat transfer due to the actual motion of the fluid itself. • Convection occurs in all fluids, whether liquids or gases.

37. Heat Transfer: Convection • Convection explains why warm air rises.

38. Heat Transfer: Convection • Convection is also responsible for breezes that occur at the beach.

39. Heat Transfer: Radiation • Radiation is the transfer of heat through electromagnetic waves.

40. Heat Transfer: Radiation • Everything (all objects!) are constantly radiating and absorbing energy.

41. REVIEW • 1. Energy from the Sun reaches Earth by: • A. Conduction and radiation • B. Radiation only • C. Conduction and convection • D. Conduction only

42. REVIEW • 2. The Second Law of Thermodynamics states that • A. No system can reach absolute zero. • B. Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred. • C. Heat never spontaneously flows from a low-temperature substance to a high temperature substance. • D. None of the above

43. REVIEW • 3. The principal reason one can walk barefoot on red-hot WOOD coals without burning the feet has to do with • A. the low temperature of the coals • B. the low thermal conductivity of the coals • C. mind-over matter techniques • D. The inability of feet to feel pain.