Chapter 10 (briefly!)Chapter 10 (briefly!)

HEAT TRANSFERHEAT TRANSFER

Energy transfer (3 TYPES)

Conduction Convection

Radiation

ConductionConductionHeat transfer from one particle to the next

– Particles at the warm end move faster and this then causes the next particles to move faster and so on.

In this way heat in an object travels from:

the HOT end the cold end

Conduction cont…Conduction cont…

Occurs when particles hitting each other and so energy is transferred.

Can happen in solids, liquids and gases

Happens best in solids-particles very close together

ConductorsConductors

Conductors: Materials that conduct heat quickly

All metals are good conductors of heat– Pans for cooking are usually made with a

copper or aluminium bottom and plastic handles (plastic is a poor conductor…you won’t get burned)

Insulators/poor conductorsInsulators/poor conductors

Insulators: materials that conduct heat slowly or poorly– Glass, wood, plastic and rubber are poor

conductors (good insulators)

ConvectionConvectionConvection: Heat transfer by movement of

fluids

Convection Currents: heat carried by the particles.

Convection CurrentsConvection CurrentsHot liquids and gases expand and rise

while the cooler liquid or gas falls (all caused by a difference in densities!)

1. Hot air rises

2. Goes across

3. Then down

4. And across

RadiationRadiation

Radiation: Transfer of heat directly from the source to the object by a wave, travelling as rays.– Heat radiation is also known as

Heat transfer by radiation does not need particles to occur and is the only way energy can be transferred across empty space

INFRA-RED RADIATION

Emission of Radiation (canned Emission of Radiation (canned heat lab 2)heat lab 2)

Hotter objects emit (give out) heatDifferent surfaces emit heat at different speedsA dull black surfaces loses energy more

quickly – it is a good radiatorA bright shiny or white surface is a poor

radiator– Survival kits have shiny heat blankets in them,

covering in a shiny blanket reduces radiation and therefore heat loss.

Emitters of heatEmitters of heat

Bright shiny canPoor radiator

Dull black canGood Radiator

Absorption of Heat (canned Absorption of Heat (canned heat lab 1)heat lab 1)Cooler objects absorb (take in) heat

Substances absorb heat at different speeds

Dull, black surfaces absorb heat quickly

Bright, shiny surfaces absorb heat slowly

In hot countries, people wear bright white clothes and paint their houses white to reduce absorption of energy from the sun.

Gas/Oil storage tanks are sprayed silver to reflect sun’s rays

AbsorbersAbsorbers

Shiny, bright canPoor absorber

Dull black canGood absorber

Evaporation is Cooling!!Evaporation is Cooling!!

Sweating is cooling…dogs have no sweat glands, so they pant

Chapter 10 bonus questionsChapter 10 bonus questions

Why is boiling a cooling process??