1. Convection

2. Material Flow  Objects at different temperatures may not be in direct thermal contact.  An intermediate mechanism is needed to transfer heat.  If the heat transfer is through the motion of a fluid, then it is called convection.

3. Fluid Motion  Objects in a fluid have a force of buoyancy.  Materials expand when they are heated. Increased volumeIncreased volume Lower densityLower density  Warm fluids generally rise. F b = mg

4. Circulation  If one area in a fluid is heated that are will become less dense.  As it moves away it transfers energy and cools  Cool fluid replaces the warm fluid that left.

5. Home Heating  Convection causes heat to circulate in a house. Water circulates in pipes Air circulates around radiators.  Forced circulation uses a fan to push heated air. Faster exchange of heat

6. Thunderstorm  Thunderstorms move heat energy with convection.  Temperature difference is between masses of warm and cold air. Warm air rises in the storm over a mass of colder air. The moisture condenses as the air cools. The cool air in the storm descends with precipitation.

7. Global Circulation  Warm air at the equator also rises.  As it moves poleward it cools.  The cool air descends.  This forms a Hadley cell.

8. Global Circulation  The rotating earth breaks up the Hadley cell.  Circulation moves heat in a complex pattern that controls the weather.

9. More Convection  Convection moves heat in many systems. Inside the oceans – ocean currentsInside the oceans – ocean currents Inside the earth – continental driftInside the earth – continental drift Inside the sun - sunspotsInside the sun - sunspots next