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Heat

Heat. The Fire Down Below. 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”. Temperature.

walter-hebert
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Heat

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  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

  6. 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

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

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

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

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

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

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

  13. 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

  14. Thermal Expansion • As substances increase in temperature, the particles move apart • Substances expand and become less dense when heated • Substances shrink and become more dense when cooled • Explains expansion joints in bridges and concrete sidewalks • Water is one very important exception

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

  16. 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, free electrons

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

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

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

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

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

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

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

  24. 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

  25. 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)

  26. Homework 26 • Pg. 163 – Questions # 1- 4 • Pg. 170 – Questions # 1 - 4

  27. 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

  28. 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

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