Presentation on theme: "S2 Revision Heat. Temperature Temperature is a measure of the hotness or coldness of something and is measured in ˚C. There are three different ways that."— Presentation transcript:
S2 Revision Heat
Temperature Temperature is a measure of the hotness or coldness of something and is measured in ˚C. There are three different ways that heat moves: –Conduction –Convection –Radiation
Conduction Heat travels through solids by conduction. Heat travels from atom to atom because the atoms in solids are close together. The heated atoms vibrate more quickly and pass the vibrations on to neighbouring atoms so spreading the heat.
Conduction Conductors are substances that let heat pass through them easily. Metals are the best conductors.
Conduction Insulators do not let heat pass through them easily. Many solids are insulators such as rubber, plastic, cork, glass and wood. Air is an extremely good insulator. Our clothes keep us warm by trapping the air between the fibres – keeping the heat in
Conduction Conductors we use in the home are pots – which conduct heat to the cooking food and radiators which provide heat for our homes. Insulators used in the home are pot handles – which stop us burning our hands. Also oven gloves and insulating jackets for hot water tanks. Our clothes are insulators to stop our bodies losing heat.
Convection Heat travels through liquids and gases by convection. Liquids and gases cannot conduct heat because the particles are close enough together to pass heat to one another.
Convection When we heat a liquid or gas a convection current is set up. The particles that are heated rise up and colder particles move in below them. The continual movement of hot and cold particles eventually heats up the whole container of gas or liquid.
When we heat air particles they move about more and spread out. They become less dense – less closely packed. The air which is less dense is ‘lighter’ than the colder air so it rises to the top.
Convection This principle is used in hot-air balloons. The hot air inside the balloons is less dense than the air outside so the balloon floats.
Radiation Lots of heat comes to us through space from the sun. Space has very few particles in it. We say that space is a vacuum.
Radiation Conduction or convection cannot take place in space because there are no particles that can vibrate or move. The heat is travelling to earth by another method called radiation. Radiation travels from the sun in straight lines in all directions
Radiation The suns rays contain many different types of radiation including ultra violet and infra red. The most important one for this course is infra red which is another term for heat.
Radiation and Surfaces Black and dark surfaces are best at absorbing heat Black and dark surfaces are best at radiating heat
Radiation and surfaces Shiny and white substances are poor at absorbing heat. Shiny and white substances are poor at radiating heat.
Radiation and Surfaces So in warm sunny countries light clothing is worn to reflect the heat. Car radiators are black in colour because that makes them better at taking heat away from the engine.
Infra-red Radiation Infra-red radiation is another word for heat. Our bodies give out infra-red radiation. This can be picked up by thermal cameras.
Infra-Red Radiation Thermal cameras can be used for finding people that are lost up a mountain at night or are trapped in a smoke filled building. Infra-red can also be used to operate TV remote controls and to trigger burglar alarms and security lights.