Transferring Thermal Transferring Thermal EnergyEnergy

Chapter 9Chapter 9

Section 3a Section 3a

Heat TransferHeat Transfer

Heat flows from hot to cold. Heat flows from hot to cold. If you hold something cold, heat flows from If you hold something cold, heat flows from

hand to object.hand to object. If you hold something hot, heat flows from If you hold something hot, heat flows from

object to handobject to handConduction-Conduction- transfer of thermal energy transfer of thermal energy

through matter by the direct contact of through matter by the direct contact of particles particles Occurs because particles are in constant Occurs because particles are in constant

motionmotionKE transferred as particles KE transferred as particles collidecollide

http://www.physchem.co.za/Heat/http://www.physchem.co.za/Heat/Transfer.htm#ConductionTransfer.htm#Conduction

ConductionConductionHeating of metal pan-Heating of metal pan-

Particles in handle of pan move slowlyParticles in handle of pan move slowlyFast moving particles from the bottom bump Fast moving particles from the bottom bump

into slower particles and speed them upinto slower particles and speed them upOccurs until all particles move the same Occurs until all particles move the same

speedspeedConduction works best in Conduction works best in solids-solids-

especially metals- because particles are especially metals- because particles are close togetherclose together

Conduction and ConvectionConduction and Convection

Metals- good conductors-because electrons Metals- good conductors-because electrons move easily & transfer KE to nearby particlesmove easily & transfer KE to nearby particles

Fluid- any materials that flowsFluid- any materials that flows ConvectionConvection- transfer of energy in a fluid by the - transfer of energy in a fluid by the

movement of heated particles movement of heated particles Convection Convection currentscurrents transfer heat from warmer transfer heat from warmer

to cooler parts of a fluid.to cooler parts of a fluid. Convection vs. Conduction- Convection vs. Conduction-

Conduction involves collisions and transfers of Conduction involves collisions and transfers of energy. energy.

Convection involves movement of the energetic Convection involves movement of the energetic particles from one location to another particles from one location to another

           

     

     

ConvectionConvection

Convection- results in changes in densityConvection- results in changes in densityAs particles move faster, they get farther apartAs particles move faster, they get farther apartFluid expands as temperature increasesFluid expands as temperature increasesLarger volume = smaller densityLarger volume = smaller densityDecreasing density results in the rise of the Decreasing density results in the rise of the

warmer fluidwarmer fluid Lava Lamp- Lava Lamp-

Cool oil = dense = sits on the bottomCool oil = dense = sits on the bottomWarmer oil = less dense than alcohol & risesWarmer oil = less dense than alcohol & risesAs it rises, it loses energy through conductionAs it rises, it loses energy through conduction

Causes decrease in density = sinkingCauses decrease in density = sinking

When oil is When oil is coolcool

Oil is warm, Oil is warm, so it risesso it rises

Oil starts to Oil starts to lose heat by lose heat by

conduction and conduction and fallsfalls

Convection CurrentsConvection CurrentsCurrents in which warm portions of the Currents in which warm portions of the

fluid move through the substance- fluid move through the substance- convectionconvection

The warm portions transfer energy to the The warm portions transfer energy to the cool section through conductioncool section through conduction

Heat Transfer on EarthHeat Transfer on Earth

At equator- earth experiences the most heat At equator- earth experiences the most heat from the sun. from the sun. Result: evaporation of water and large accumulations Result: evaporation of water and large accumulations

of clouds. of clouds. As the water vapor rises, it cools and condenses, As the water vapor rises, it cools and condenses,

forming rain forming rain

After the rain = dry airAfter the rain = dry air Dry air causes moisture to evaporate, drying out the Dry air causes moisture to evaporate, drying out the

ground – causes desertground – causes desert

Convection currents create Convection currents create desertsdeserts and and rain rain forestsforests over different regions of Earth over different regions of Earth