Heat

1. Heat The Fire Down Below

2. Heat • A flow of energy from objects of higher thermal energy to objects of lower thermal energy • Heat is measured in Joules (J) because it is a form of energy • Described as a flow from hot to cold • No such thing as “cold”

3. Temperature • Based on the motion of the particles in a substance • Fast motion = high temperature • Slower motion = lower temperature • Relatively describes how the particles collide with the surface of the thermometer • Collisions transfer energy

4. Temperature Scales • Fahrenheit • Common in the US • Freezing point of water is 32ºF • Boiling point of water is 212ºF • Celsius • Common in the rest of the world (SI) • Freezing point of water is 0ºC • Boiling point of water is 100ºC

5. Temperature Scales • Kelvin • Used for science, as there are NO negative values • 0K is set at Absolute Zero, the temperature at which all particle motion stops • Freezing point of water is 273K • Boiling point of water is 373K • NOTE – 100K between freezing and boiling, so Kelvin uses the same degrees as Celsius

7. Converting Temperatures • Fahrenheit to Celsius Cº = 0.55 (Fº - 32º) • Celsius to Fahrenheit Fº = (1.8 x Cº) + 32º • Celsius to Kelvin K = C + 273 Adjusts for differences in Zero temperature

8. Because heat is a form of energy, heat is measured in … • Watts • Newtons • Joules • Mishbohah

9. Heat always flows… • From low E to high E • From high E to low E • Across layers of density • Downwards, like gravity

10. The average motion of particles in a substance defines that substance’s… • Heat • Energy • Potential Energy • Temperature

11. The temperature scale used in the USA is • Fahrenheit • Celsius • Kelvin • Thermocline

12. The temperature scale used in SI is • Fahrenheit • Celsius • Kelvin • Thermocline

13. The temperature scale used in science is • Fahrenheit • Celsius • Kelvin • Thermocline

14. Thermal Energy • Usually based on the total number of particles, as most temperatures in which we survive are relatively close together (-15ºF to 130ºF) • More particles = more thermal energy • Ex. boiling cabbage, frying foods, ocean water

15. Heat Transfer • Conduction • HTB direct particle contact • Convection • HTB mass movement of particles • Radiation • HTB invisible infrared radiation

16. Conduction • Heat transfer by direct particle contact • The particles of the higher energy material vibrate more rapidly • As they collide with the lower energy material, some of the particles increase speed • Eventually, all the particles vibrate at the same speed • Mix hotter and colder materials? The temperature moderates…

19. More on conduction…

20. Convection • Heat transfer by mass particle movement • The particles of the higher energy material vibrate more rapidly, and • Thermal expansion causes the particles of the hotter material to become less dense • The warmer, less dense material rises, • The cooler, more dense material sinks

22. Above and Below… • Inside the Earth, heat from Earth’s core moves towards the surface through the plastic mantle

23. Above and Below… • The atmosphere and hydrosphere move heat through convection in weather and ocean currents

24. Radiation • Heat transfer by invisible, electromagnetic waves • Infrared waves are given off because of particle motion or electrons changing energy levels during reactions • The waves released can be absorbed by other particles, interpreted as heat

25. Feel the heat! • The Earth is warmed by infrared radiation from the Sun • NO HEAT IS RECEIVED FROM THE SUN BY DIRECT PARTICLE CONTACT

27. What type of heat transfer describes cooking on an electric range? • Conduction • Convection • Radiation

28. What type of heat transfer describes why a dark shirt feels warmer on sunny days? • Conduction • Convection • Radiation

29. What type of heat transfer describes how a A/C system changes room temperature? • Conduction • Convection • Radiation

30. What type of heat transfer describes how lake water is hot on top and cold on bottom? • Conduction • Convection • Radiation

31. What type of heat transfer describes cooking in an electric oven? • Conduction • Convection • Radiation

32. Thermos bottles… • Reduce heat flow in BOTH directions • Vacuum eliminates convection, conduction • Inner bottle is usually reflective to reduce radiation

33. Specific Heat • Amount of energy that has to be lost or gained by a substance to change temperature • Note: Water has an incredibly high specific heat value due to the bonds between water molecules • Ammonia has a higher specific heat, but you can’t use it to cook!

35. Specific Heat Q = m c T where m is the mass of the substance c is the specific heat value T is the change in temperature of the substance (Tfinal – Tinitial)

36. More on Radiation • Emitters are substances that give off radiation • Stars, campfires, space heaters, etc. • Absorbers capture radiation • Black shirts, asphalt, water • Reflectors return most of the radiation that is emitted towards them • Mirrors, aluminum foil, ice & snow

37. Thermal Expansion • As substances increase in temperature, the particles move apart • Essentially Charles’s Law: • As temperature increases, volume increases • As temperature decreases, volume decreases • Substances expand and become less dense when heated • Substances shrink and become more dense when cooled

38. Thermal Expansion • Explains expansion joints in bridges and concrete sidewalks • Water is one very important exception • As liquid water freezes to become ice, the water molecules arrange in to a lattice with air spaces • ICE FLOATS BECAUSE IT IS LESS DENSE • Density of liquid water = 1g/cm3 • Density of ice = 0.92 g/cm3

39. Examples of Thermal Expansion • Notice the cracks that have formed in the concrete after some time of thermal expansion

40. Conductors • Allows heat (and electricity) to flow easily with little or no resistance • Heats up quickly, cools down quickly • Low “Specific Heat” • Usually metals • High density (no air spaces), free electrons

41. Insulators • Resist the flow of heat (and electricity) • High “Specific Heat” • Designed to trap “dead air” spaces • Resisted heat can build up and cause the substance to burn • Usually nonmetals • Large molecules, no free electrons

42. Layers and Heat Transfer • Layers trap air in a “dead air space” • More layers mean it’s harder to change temperatures between layers • Ex. double-paned windows, dressing in layers, layers of construction on a house

43. Combining insulation • Notice the pipes wrapped in “fluffy” insulation, but the outside is shiny. • The “fluffy” traps “dead air” spaces where the shiny inhibits radiation

44. Why are gaps designed in bridges, roads and sidewalks? • As temperatures drop, the materials contract • As temperatures rise, the materials expand • To save money on the project by reducing the amount of materials • None of the above

45. Which type of heat transfer is impeded by reflective materials ? • Convection • Conduction • Radiation • None of the above

46. Which type of window would be the best insulator for your home? • Single-paned • Double-paned • Triple-paned • Wooden shutters

47. Which type of heat transfer is impeded by materials that trap “dead air” spaces ? • Convection • Conduction • Radiation • None of the above

48. Which type of heat transfer is impeded by vacuums and gaps in designs ? • Convection • Conduction • Radiation • None of the above

49. Explain these… • Why was the Amundsen-Scott Antarctic Station is built to be half under the ice? • Why do desert-dwelling peoples wear a dark outer layer on top of their inner layers?

50. Explain these… • Why would a hunter “dress in layers” the way your parents always suggest? • What can you infer about the parts of the roof of this house that have no snow?