1 / 29

Understanding Heat Transfer and Thermal Energy

Learn about heat transfer, thermal energy, temperature scales, and examples of thermal expansion. Understand conductors, insulators, heat transfer types, and specific heat. Explore layers, radiation, and heat emitters and absorbers.

walter-hebert
Télécharger la présentation

Understanding Heat Transfer and Thermal Energy

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related