Convection Currents

Let’s Start With Density High density: molecules close together in a certain volume Low density: molecules far apart in a volume

High Temperature and Density When molecules get hotter, they get more energy They start to move around more They spread out LOW density

Low Temperature and Density When molecules have a lower temperature, they have less energy They don’t move around as much They get closer together HIGH density

Densities for Different States of Matter

Mixtures of High and Low Densities Oil: less dense than water, so it rises to the top. Water: more sense, so it sinks to the bottom.

Radiators

How a Radiator Works Since cool air sinks (it is MORE dense), it falls to the bottom of the room next to the radiator. The radiator heats the air, which rises because it becomes LESS dense. Once the hot air loses energy, it becomes MORE dense again and sinks… and the cycle starts over again.

Think About It --- When you open the refrigerator, does the cold air that comes out rise to the top of the room or fall to the floor? In winter, what happens to the hot air produced in your heater; does it rise to the ceiling or fall to the floor of the room? In the summertime, is it cooler to sleep in an upstairs room or in a basement?

Convection Current Video Clip Watch this video demonstration of convection currents. The red water is hot water, and the blue water is ice-cold water.

Convection Currents in the Earth

Questions to Think About What provides the heat for convection currents in the mantle? What cools the mantle down before it begins to sink?