Dark, matt surfaces are
best at absorbing and
emitting infrared
radiation
Light, shiny surfaces are
worst at absorbing and
emitting infrared radiation
and reflect a lot of the
radiation
If an object is cooler than its
surroundings it will absorb more
infrared radiation than it emits
If an object is warmer
than its surroundings it
will emit more infrared
radiation than it absorbs
Everything absorbs and emits
infrared radiation
Kinetic Theory
Gases
Almost no forces of attraction
Particles move in a random direction at high speeds
High energy levels
Solids
Strong forces of
attraction keep it in a
fixed pattern
Low amount of
energy so it can
only vibrate in
fixed positions
Liquids
Weak forces of attraction
The particles can move in random directions at low speeds
Conduction
A type of heat
transfer that
occurs mainly
in solids but
also in liquids
and gases
The particles vibrate and transfer
their heat energy to neighbouring
particles
More dense materials are
better conductors because their
particles are closer together
Materials that have
particles that are
far apart transfer
heat via conduction
slower and are
known as insulators
Metals are good conductors because
they contain free electrons which allows
them to transfer energy faster
Convection
Occurs mainly in liquids and gases
Particles vibrate more as they
heat up and so take up less
space and become less dense
Less dense
particles rise
taking the energy
with them
Convection currents
occur when the less
dense particles rise
and are replaced by
the denser particles
Condensation
Condensation is the process of turning a gas into a liquid
If particles lose energy they slow down and the attractive
forces between them grow stronger and if the forces are
strong enough the particles join and become a liquid
Factors affecting the rate of condensation
Temperature of the surface the gas touches
Airflow
Density of gas
Temperature of the gas
Evaporation
Evaporation is the process of a liquid turning into a gas
If the particles have enough
energy and are travelling in the
right direction they can escape the
attractive forces of the other
particles and evaporate
Factors affecting the rate of evaporation
Airflow over the liquid
Surface area of the liquid
Temperature of the liquid
Density of the liquid
Rate of Heat Transfer
Factors affecting rate of heat transfer
Surface Area
Type of material
Colour
Surface area to volume ratio
The smaller this is, the faster the transfer
Controlling Heat Transfer
Vacuum Flask
The flask uses two walls to create a
vacuum to stop heat loss through
conduction and convection
The flask walls are silver and
shiny to stop heat loss through
radiation
The insulated support stops the
flask walls from cracking under
the pressure and minimises heat
loss from conduction
The stopper is made of plastic and filled with cork and
foam to reduce heat loss through conduction
Humans and Animals
Hairs on your skin
stand up to trap a
thicker layer of
insulating air to limit
heat transfer by
convection
Blood is diverted to
the surface where
heat can be lost as
radiation resulting in
pinker skin tone
Arctic foxes have small ears to minimise heat loss via radiation
Desert foxes have large ears to maximise heat loss via radiation