9 Physics - Energy and Matter

When you heat up something the particles speed up, the vibrations take up more space, making it expand in all directions.

Gases expand the most, then liquids, then solids

The volume of a gas depends on the container it is in

Gap left on a bridge Glass dish put in an oven would crack Thermometer Bimetal strip (pg 105) Water when cooled (solidified) expands (pg 105) Bimetal thermostat (when temp rises, the bimetal strip bends and the contacts separate, current to heater is cut off, when temp. falls the opposite happens)

Overhead cables are left slack, to allow for contraction that would happen on a cold day

At a fixed pressure, as the temp increases, the volume increases directly proportional

Thermal conduction - one end of an object is heated, the heat is transferred to the colder end, as faster particles bump onto the slower ones, making them move

insulators

Conductors: -Metals -Silicon Graphite Insulators: • Glass • Water • Plastics • Rubber • Wood • Materials containing trapped air (wool, plastic foam, polystyrene)

• A pan might have a copper bottom but a plastic handle so you don’t burn your hand • Birds fluff up their feathers to trap more air • It´s safer to pick hot dishes with a dry cloth than a wet one because it has air trapped in it

• Plastic foam lagging round a hot water storage tank • Glass or mineral wool insulation in the loft • Wall cavity filled with plastic foam, or wool • Double-glazed windows: 2 sheets of glass with air in between

Convection

Liquid: Potassium permanganate in one side of beaker filled with water, heat that side of beaker, p.p. moves up and to the other side Gas: In a box, have cold ice in one side and burning tissue and warm rocks on the other, smoke will move up, to the cold side, then down, and repeat

Room with radiator Windy by the sea Hot water system Refrigerator

During the day the sand is hotter, the war air rises (less dense), it moves towards the sea (less pressure), cools again (more dense), falls, creating wind towards coast

Thermal radiation Mainly infrared waves

Sending out : emitters Taking in : absorbers Good emitters are also good absorbers

MATT BLACK WHITE SILVER emitters best———————————-worst reflectors worst———————————-best absorbers best———————————-worst (note that silver is a bad emitter and absorber because it reflects most of the thermal radiation away, while matt doesn’t)

2 metal plates with diff surfaces are placed at the same distance from a radiant heater. To find which absorbs more, measure the rise in temperature (pg. 112)

Metal cube filled with boiling water, heats the surfaces to the same temp. Thermal radiation detector is placed in turn at the same distance from each surface and the metre readings are compared

The suns´s thermal radiation passes easily through glass or plastic, the ground inside warms up and heats the air. Hot air cannot escape

• If you live in a desert you would want a white or silver car • Radiators are painted white to look nicer but matt black would be a better choice as it is good at emitting heat • Bears have black skin because it absorbs heat well, and white fur because it is a poor emitter, thick fur also traps air(insulator) • Our body gives energy by radiation • Sun heats the earth

Convection: -diff temps in an oven, uncooked food Convection: -can lead to burning Radiation: heat lost to environment, requires constant source of energy

Bay Marie (hot water bath) • Radiation: fire heats the pan • Conduction: heat is absorbed by the pan • Convection: heat from pan goes to the water, through air, and to the food