Transcript HEAT ENERGY

THERMAL (HEAT) ENERGY
What is HEAT?
• Particles move around more and take up
more room if heated – this is why things
expand when they’re hot
• It is also why substances change from:
solids
liquids
gases
when heated
Heat and Temperature
The temperature of an object tells us how
HOT it is
 Measured in degrees Celsius - °C
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Heating and Cooling
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If an object has become hotter,
it means that it has gained heat energy.

If an object cools down, it means it has
lost energy
Heating and Cooling cont…
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Thermal energy always moves from:
HOT object
COOLER object
HEAT ENERGY
3 Types of Thermal Energy Transfer
Conduction
Convection
Radiation
Conduction
Heat is transferred through a material by
being passed 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
Conduction cont…
Occurs by the particles hitting each other
and so energy is transferred.
 Can happen in solids, liquids and gases,
 Happens best in solids, where particles
very close together
 Conduction does not occur very quickly in
liquids or gases

Conductors
Materials that conduct heat quickly are
called conductors
 All metals are good conductors of heat
 Copper and aluminium are very good
conductor of heat
 Pans for cooking are usually made with a
copper or aluminium bottom and plastic
handles

Insulators/Poor Conductors
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Materials that conduct heat slowly or poorly are
called insulators
Glass, wood, plastic and rubber are poor
conductors (good insulators)
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 refrigerator has insulation material around it to
keep it cold – it reduces amount of heat conducted
to inside from the warmer room
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
 Occurs because an area with warm particles
expands and becomes less dense than the
cooler areas nearby. The warm particles rise.
Cooler particles fall into the space left by the
warm particles. This process is called a
convection current.

Convection Currents

Hot liquids and gases expand and rise
while the cooler liquid or gas falls
2. Goes across
3. Then down
1. Hot air rises
4. And across
Convection cont…
The sun can cause large convection
currents - WINDS
 During daytime the land warms up more
than the ocean. The warm air rises over
the land and cool air falls over the ocean,
so we feel a sea breeze.
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Radiation
Transfer of heat directly form the source to the
object by a wave, travelling as rays
 Thermal radiation is also known as
INFRA-RED RADIATION
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All objects that are hotter than their surroundings
give out heat as infra-red radiation.
 Heat transfer by radiation is the only way energy
can be transferred across empty space.

Thermal Radiation
Bright shiny materials
are poor radiators
Dull dark materials are
good radiators
Absorbers
Shiny, bright can
Poor absorber
Dull black can
Good absorber
Key Words
Temperature
Cold
Insulator
Radiation
Transfer
Heat
Convection
Conduction
Conductor