Transfer of Heat. This will continue until all have reached the same equilibrium temperature.

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1 Transfer of Heat When objects at different temperatures come in close proximity, heat will spontaneously transfer from the warmer object to the cooler objects. This will continue until all have reached the same equilibrium temperature. Heat transfers in 3 different ways: conduction, convection, and radiation.

2 Conduction Conduction is where fast moving molecules bump into the neighboring molecules and get them moving faster as well. The heat is passed on down the line. Conduction works best in solid objects. The tile floor feels colder than the wooden floor even though they are both at the same temperature. Tile conducts heat out of your feet faster than wood does.

3 Conduction and Heat Loss Snow patterns on the roof of a house show areas of poor insulation. It is in these places that heat is rapidly conducted out of the house.

4 Convection A heated fluid becomes less dense and rises, whereupon it cools and sinks. Heat moves along the convection loop of fluid in motion. Heated air rises to the ceiling, where it cools and then sinks to the floor, only to become heated again.

5 Creation of a Lake Breeze Convection currents are produced by the unequal heating of land and water. During the day, the land heats up faster than the water. Hotter air over the land becomes less dense and rises. Air over the water cools, becomes denser and sinks. A cool breeze from the water blows toward the land to complete the loop.

6 Radiation In the form of radiation, heat travels as waves of electromagnetic energy. Radiant heat forms shadows and can be reflected just like light. It is the only way to move heat through a vacuum. Infrared radiation is detectable to us as heat.

7 Both the Sun and Earth emit the same kind of radiant energy. The Sun's glow is visible to the eye. Earth's glow consists of longer (infrared) waves and isn't visible to the eye. Radiation

8 Absorption of Radiant Energy Good emitters of radiant energy are also good absorbers; poor emitters are poor absorbers. When the black rough-surfaced container and the shiny polished one are filled with hot (or cold) water, the blackened one cools (or warms) faster.

9 The Thermos Bottle A thermos bottle is a doublewalled glass container with a vacuum between its silvered walls. The vacuum inhibits conduction and convection from occurring. Heat loss by radiation is prevented by the silvered surfaces which reflect radiant energy back into the bottle.

10 Changes of Phase We will refer to 4 phases of matter: Solids in which molecules can only vibrate in their assigned places. Liquids in which molecules are free to move around but are still strongly attracted to their neighbors. Gases in which molecules are far apart and move quite independently. Plasmas which consist of ions and electrons moving at high speed.

11 Change in Phase Evaporation is the transition from liquid to gas. Water evaporating from your body takes energy with it, cooling you in the process. Evaporation is a natural cooling process.

12 Changes in Phase Condensation is the transition from gas to liquid. Condensation is a warming process. Internal energy is released by steam when it condenses into liquid water inside this 'radiator'.

13 Changes in Phase Evaporation naturally occurs at the surface of a liquid. You can make a liquid change to a gas below the surface by adding heat. This is called boiling. During boiling, gas bubbles form below the surface and expand as they rise upward due to decreasing water pressure upon them.

14 Changes in Phase If evaporation is a cooling process, then shouldn't boiling also have a cooling effect? Logic tells us that it should be so, but somehow it just doesn't seem right! So what's really happening?

15 Changes in Phase It's true. Boiling does have a cooling effect on the water, but the heat we add at the bottom makes up for it by adding heat to the water. These two effects cancel each other out. The end result is that the water's temperature stays constant!

16 Changes in Phase Adding heat to a mixture of water and ice at 0 C melts the ice without changing the temperature of the mixture. The heat required to change the phase at constant temperature is called latent heat.

17 Changes in Phase The level portions of the graph line show where the temperature stays constant during a phase change.

18 Changes in Phase Freezing occurs when a liquid changes to a solid. As energy is removed, molecular motion slows until attractive forces are able to bind molecules together. Foreign molecules interfere with crystal formation, requiring slower molecular motion (colder temperatures). This is why adding rock salt to ice, lowers its freezing temperature.