Heat and temperature

1. Heat and temperature

2. Kinetic molecular theory • What do we know about how particles in a substance behave?

3. Phases of matter - solids • Definite shape and volume • Rigid 3-D structure • Allowed motions restricted to vibration in place only

4. Phases of matter - liquids • Definite volume, indefinite shape • Allowed motions • Vibration • Rotation • Limited translation

5. Phases of matter - gases • Indefinite volume and shape • Allowed motions • Vibration and rotation • Translation on random, mostly free paths

6. Temperature • How cold or hot a substance is • Thermometers • Used to measure temperature What are the parts of a thermometer? How does a thermometer work?

7. Fahrenheit & Celsius The Common Temperature Scales • Celsius & Kelvin

8. Temperature scales • Defined w.r.t various reference points • Fahrenheit • Celsius • Kelvin • Conversion formulas • Fahrenheit to Celsius • Celsius to Fahrenheit • Celsius to Kelvin

9. supernova core 100,000,000,000 K core of sun 15,000,000 K surface of sun 6,000 K lava 1,200 K Room temperature 294 K triple point cell 273.16 K ice 273 K dry ice 164 K liquid nitrogen 77 K liquid He 4 K Universe 2.7 K dilution refrigerator 0.003 K 1848 William Thomson a.k.a. Lord Kelvin 0 K absolute zero

10. Absolute Zero (0K)

11. Thermal Expansion • Most solid materials expand or contract depending on their temperature: • As T increases object expands • As T decreases object contracts

12. What’s happening? • How does the particles of the liquid in the thermometer behave when it touches a cold object? • How about a warm object?

13. Ring and Ball • Observations? • Explanations?

14. Heat • A form of energy transfer between two objects due to difference in temperature • Which was colder, the metal or the wood in the room? How about the alcohol?

15. Heat versus temperature Temperature • A measure of hotness or coldness of an object • Based on average kinetic energy Heat • Based on total internal energy of molecules • Doubling amount at same temperature doubles heat • Flows from high to low temperature

16. HEAT Form of energytransfer from hot to cold Relates to the total energy of the particles in a substance Unit of measurement: -Calories or Joules TEMPERATURE How hot or cold something is Relates to the average KE of the particles in a substance Unit of measurement: - Deg Celsius or Farenheit or Kelvin So what’s the difference?

17. Heat Transfer Mechanisms

18. Heat Transfer Mechanisms • Conduction:heat flow through materials • Convection:heat flow through moving fluids • Radiation:heat flow through light • All three transfer heat from hot to cold

19. - - - - - - - - - - - - - - - - - Cu+ Cu+ Cu+ Cu+ Cu+ Cu+ Cu+ Cu+ Cu+ Cu+ Cu+ Cu+ Cu+ Cu+ Cu+ Cu+ Cu+ Conduction

20. Conduction • Heat flows through material, atoms don’t! • In an insulator: • adjacent atoms jiggle one another • atoms do work, yielding microscopic exchanges of energy (typically slow) • In a conductor, • mobile electrons carry heat • heat flows quickly, over long distances via mobile electrons

21. Convection

22. Convection • Fluid transports heat (thermal energy stored in atoms) • Fluid warms up near a hot object • Fluid cools down near a cold object • Natural buoyancy* drives convection • Warmed fluid rises away from hot object • Cooled fluid descends away from cold object • *”less dense things float”…

23. Radiation • Heat transferred by electromagnetic waves(radio, infrared, microwaves, light, …) • Higher temperature yields more radiated heat Infrared radiation

24. Specific heat Variables involved in heating • Temperature change • Mass • Type of material • Different materials require different amounts of heat to produce the same temperature change