Convection and the Convection and the MantleMantle

How is heat transferred?How is heat transferred?

What makes an object hot?What makes an object hot?

Movement of Movement of particlesparticles

Heat moves toward Heat moves toward colder areascolder areas

3 3 Types of Heat TransferTypes of Heat Transfer

RadiationRadiation

ConductionConduction

ConvectionConvection

RadiationRadiation

Transfer of energy through spaceTransfer of energy through space

No direct contact between heat No direct contact between heat source and an object.source and an object.

Can you think of examples of Can you think of examples of Radiation?Radiation?• Sunlight warming us during the daySunlight warming us during the day• Being warmed by a fireBeing warmed by a fire

ConductionConduction

Heat transfer within Heat transfer within a material, or a material, or between materials between materials that are touching.that are touching.

The particles heat The particles heat up, move faster, up, move faster, and bump into and bump into other particles that other particles that do the same.do the same.

Conduction: ExamplesConduction: Examples

A spoon sitting in a A spoon sitting in a boiling pot of soup.boiling pot of soup.

Hot sand at the Hot sand at the beach.beach.

Cold hands after Cold hands after making a snow making a snow ball.ball.

ConvectionConvection Heat is transferred by the movement Heat is transferred by the movement

of fluids and gases. of fluids and gases. Heated particles begin to flow, and Heated particles begin to flow, and

transfer heat from one particle to transfer heat from one particle to another.another.

This is caused by differences in This is caused by differences in temperature and density* in a fluid.temperature and density* in a fluid.• Density = a measure of how much mass Density = a measure of how much mass

there is in a substance. Example: Rock there is in a substance. Example: Rock is much denser than water.is much denser than water.

Convection CurrentsConvection Currents

How does hot liquid move?How does hot liquid move? Think of the boiling pot of soup:Think of the boiling pot of soup:

• The soup on the very bottom of the pot The soup on the very bottom of the pot is the hottest, and therefore, less dense. is the hottest, and therefore, less dense. It begins to float towards the top. It begins to float towards the top.

• Once at the top, it cools, which Once at the top, it cools, which increases its density. It becomes increases its density. It becomes heavier, and due to gravity, falls back to heavier, and due to gravity, falls back to the bottom of the pot.the bottom of the pot.

Convection currents take on a circular Convection currents take on a circular motion. motion.

This is how the mantle rock moves inside This is how the mantle rock moves inside the earth.the earth.

Changes in DensityChanges in Density

The heating and cooling of a fluid changes The heating and cooling of a fluid changes its density.its density.

• What a fluid is heated, it’s particles move What a fluid is heated, it’s particles move farther apart at a faster speed than when it farther apart at a faster speed than when it was cold. As the particles spread out they take was cold. As the particles spread out they take up more space.up more space.

• The particles of the fluid are now being The particles of the fluid are now being stretched over a larger area, and therefore, the stretched over a larger area, and therefore, the density of the fluid decreases.density of the fluid decreases.

Inside the EarthInside the Earth

Heating and cooling of a fluid, Heating and cooling of a fluid, changes in the fluid’s density, and changes in the fluid’s density, and the force of gravity combine to set the force of gravity combine to set convection currents in motion.convection currents in motion.

Heat from the core and mantle Heat from the core and mantle causes these types of convection causes these types of convection currents in the mantle.currents in the mantle.

The flowing mantleThe flowing mantle

Plumes of mantle rock rise slowly Plumes of mantle rock rise slowly from the bottom of the mantle from the bottom of the mantle toward the top.toward the top.

The hot rock eventually cools, and The hot rock eventually cools, and sinks back through the mantle.sinks back through the mantle.

This cycle of rising and sinking is This cycle of rising and sinking is repeated over and over.repeated over and over.

This has been happening inside our This has been happening inside our earth for more than 4 billion years!earth for more than 4 billion years!

Convection Currents in Action:Convection Currents in Action:

http://duedall.fit.edu/wholeearth/PHysical%20geology%20animations/0053.swf