transferring thermal energy chapter 9 section 3a
TRANSCRIPT
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