Heat is a form of
It travels from a hot region towards a cooler one.
Effects of heat
How heat travels
Heat can move three ways:
Conduction Convection Radiation
Through solids by conduction
Metals are good conductors of heat
Non metals are poor conductors of heat (insulators)
|Heat being conducted along a copper rod
Tthe heat makes the copper atoms vibrate faster.
These atoms in turn make the atoms near them vibrate faster.
In this way the heat energy is gradually transferred along the rod from the hot end towards the cooler end.
We can demonstrate this by coating the rod in wax and timing how long it
takes the wax to melt.
Examples and uses
Good conductors of heat: Copper, gold, Aluminium
Insulators (poor conductors): Wood, plastic, glass, china, cork
A saucepan is made of aluminium or copper which is a good conductor of heat.
The handle is made of plastic or wood which is a poor conductor
Through gas or liquid (fluids) by convection
As a liquid or gas heats up its particles move faster and get further apart.
This makes it less dense (lighter) so it starts to rise.
The rising air or water is called a convection current
|Air in a room is warmed by convection currents
is warmed by the heater.
This diagram shows how the heater warms all the air in the room.
A large city or a desert will warm air in the same way as the heater.
Examples and uses
1. Hot water rises to the top of a hot water tank. This helps in central heating in a house.
2. A radiator works by warming the air which rises and flows around the room.
3. Wind (or breezes) are often caused by hot air rising above a hot desert or city.
Cooler air travels in from the side to take the place of the warmer air
Through space by radiation
Radiation is the only form of heat that can travel through a vacuum.
Heat radiation, like light, is made of waves and travels in straight lines.
Heat from the sun reaches us by radiation
The sun gives out a large amount of radiation.
Some of it is visible (we call it light)
The heat radiation is easily stopped by anything which gets in its way like clouds.
Examples and usesHeat from the sun reaches us by radiation An electric grill heats food by radiation
More about Heat Radiation
Shiny or white surfaces do not radiate heat well which is why water in a shiny jug will stay warm longer than one in a black jug.
Dark or dull surfaces absorb heat radiation much more
easily than white shiny surfaces.
This is why in hot countries the houses and clothing are often white because white reflects the heat better.
Investigating how effective cups
are at keeping water hot
Aim: to see which cup keeps water hot the longest
|Cup 1||Cup 1
Cup 1 is made of metal painted black. It has no lid and no saucer.
Both cups are the same size and both are filled with boiling water at the same time.
1. In which cup will the water remain hot the
1. The water will remain hot for longer in cup 2
In cup 2:
The lid stops convection currents. The air heated by the coffee cannot rise
The white, shiny surface does not radiate heat well.
Cork is a poor conductor of heat so heat cannot travel down into the table.
3. The cups are the same size
The water is at the same temperature for each cup at the start.
4. A thermometer and stop watch
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