2Energy transfer (3 TYPES) Conduction Convection Radiation HEAT TRANSFEREnergy transfer (3 TYPES) Conduction Convection Radiation
3Conduction Heat 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
4Conduction cont…Occurs when particles hitting each other and so energy is transferred.Can happen in solids, liquids and gasesHappens best in solids-particles very close together
5Conductors Conductors: Materials that conduct heat quickly All metals are good conductors of heatPans for cooking are usually made with a copper or aluminium bottom and plastic handles (plastic is a poor conductor…you won’t get burned)
6Insulators/poor conductors Insulators: materials that conduct heat slowly or poorlyGlass, wood, plastic and rubber are poor conductors (good insulators)
7Convection Convection: Heat transfer by movement of fluids Convection Currents: heat carried by the particles.
8Convection CurrentsHot liquids and gases expand and rise while the cooler liquid or gas falls (all caused by a difference in densities!)2. Goes across3. Then down1. Hot air rises4. And across
9RadiationRadiation: Transfer of heat directly from the source to the object by a wave, travelling as rays.Heat radiation is also known asHeat transfer by radiation does not need particles to occur and is the only way energy can be transferred across empty spaceINFRA-RED RADIATION
10Emission of Radiation (canned 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 radiatorSurvival kits have shiny heat blankets in them, covering in a shiny blanket reduces radiation and therefore heat loss.
11Emitters of heat Bright shiny can Poor radiator Dull black can Good Radiator
12Absorption of Heat (canned heat lab 1) Cooler objects absorb (take in) heatSubstances absorb heat at different speedsDull, black surfaces absorb heat quicklyBright, shiny surfaces absorb heat slowlyIn 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
13AbsorbersShiny, bright can Poor absorberDull black can Good absorber
14Evaporation is Cooling!! Sweating is cooling…dogs have no sweat glands, so they pant
15Chapter 10 bonus questions Why is boiling a cooling process??