Heat Energy

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Nearly all liquids including water are poor conductors (good insulators)

Gases, including air are poor conductors,e.g., wool feels warm because it traps a lot of air

A fridge has insulation material round it to keep it cold – reduces amount of heat conducted to inside from the warmer room

Slide 10

Convection

Takes place in material where particles can move around inside the material, i.e. liquid or gas

The heat is carried by the particles themselves moving Convection currents

Occur because an area with warm particles expands and becomes less dense than the cooler areas nearby. The warm area rises. Cooler particles fall into the space left by the warm particles and convection current is set up

Slide 11

Convection Currents

Hot liquids and gases expand and rise while the cooler liquid or gas falls

1. Hot air rises

2. Goes across

3. Then down

4. And across

Slide 12

Convection cont…

The sun can cause large convection currents - WINDS

During daytime the land warms up more than the sea. The warm air rises over the land and cool air falls over the sea. So we feel a sea breeze.

Rising convection currents can be uses by glider pilots to keep their planes in the air and by birds to stay aloft.

Slide 13

Radiation

Transfer of heat directly form the source to the object by a wave, travelling as rays.

Heat radiation is also known as

All objects that are hotter than their surroundings give out heat as infra-red radiation

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

Slide 14

Emitters

Hotter objects emit (give out) heat

Different surfaces emit heat at different speeds

A dull black surfaces loses energy more quickly – it is a good radiator

A bright shiny or white surface is a poor radiator

Marathon runners need to keep warm at the end of races, covering in shiny blankets reduces radiation and therefore heat loss.

Slide 15

Emitters of heat

Bright shiny can Poor radiator

Dull black can Good Radiator

Slide 16

Absorbers

Cooler objects absorb (take in) heat

Substances absorb heat at different speeds

Dull, black surfaces absorb heat quickly

Bright, shiny surfaces absorb heat slowly