1. Transmission of Heat

2. Conduction of heat Takes place within certain materials and from one of these materials to another when they are in direct contact. Conductors: metals- silver, copper, aluminum and iron Insulators: delay the transfer of heat. Ex. Wood, cork, styrofoam Poor conductors are good insulators. Liquids and gases in general are good insulators. Snow is a good insulator (has a lot of air) Insulation delays the transfer of heat. Cold is the absence of heat.

3. Convection: heating occurs by currents in a fluid (liquid or gas) Convection is an application of archimedes principle. If a fluid is heated from below, it expands and becomes less dense and rises. Winds: result from convection currents that stir the atmosphere. Radiation Heat from the sun warm’s the earth’s surface through radiation. Energy that is transmitted by radiation is called radiant energy. Heat_Transmission__Conduction__Convection__and_Ra diation.asf

4. Forms of radiant energy: radio waves, microwaves, infrared, visible light, ultraviolet, X rays, and gamma rays. Absorption of radiant energy Good absorbers of radiant energy reflects very little radiant energy, including light. Thus, appears black. Ex. Pupil of eye Good reflectors are poor absorbers. Light colored objects reflect more light and heat than dark-colored ones.

5. Emission of radiant energy Good absorbers are good emitters; poor absorbers are poor emitters. Ex. A radio antenna built to emmit radio waves, will also be a good receiver of radio waves. Whether a surface plays the role of emitter or absorber depends on whether its temperature is above or below room temperature. Read p329.

6. Newton’s Law of cooling The rate of cooling of an object depends on how much hotter the object is than the surroundings. Newton’s Law of cooling states: The rate of cooling of an object- whether by conduction, convection, or radiation- is approximately proportional to the temperature difference,  T, between the object and its surroundings.

7. The greenhouse effect Radiant energy from the sun warms the earth. And earth emits terrestrial radiation which most escapes to outer space. Much of terrestrial radiation is absorbed by water vapor and carbon dioxide in the atmosphere. Effects_of_Global_Warming_on_Alaska.asf

8. Transmission of Heat