Transcript Understanding Heat Transfer, Conduction, Convection and

Thermal Energy Transfer
6th grade science
Reese
Temperature
• Temperature measures the average kinetic
energy of the particles in a substance. The
more KE the higher the temperature.
• How HOT or COLD an object is.
Heat Transfer and Fact
• Heat is the transfer of thermal energy
between substances at different
temperatures.
• When objects are heated, their particles move
faster and take up more space so they
EXPAND. When heat is released from object,
the particles slow down they CONTRACT.
Important Temperatures
• 0 C = 32 F (Freezing Water)
• 100 C = 212 F (Boiling Water)
• 37 C = 98.6 F (Body Temperature)
Temperature Scales
HEAT FLOW: HEAT ALWAYS FLOWS
FROM WARMER TO COOLER
UNTIL THERMAL
EQUILIBRIUM IS REACHED!
Heat Flow
Human bodies work
differently. We do not
reach equilibrium with
our environment
because our bodies
help regulate
temperature. We can
feel temperature changes
though…
Conduction
• Conduction is the transfer of heat through
materials by the direct contact of matter.
• Dense metals like copper and aluminum are
very good thermal conductors. Solids usually
are better heat conductors than liquids, and
liquids are better conductors than gases.
Conduction Example
Conduction Example
Thermal Insulator
• A thermal insulator is a material that conducts
heat poorly.
• Heat flows very slowly through the plastic so
that the temperature of your hand does not
rise very much.
Thermal Conduction
Thermal Conduction
Why does metal feel colder than wood, if they
are both at the same temperature?
Metal is a conductor, wood is an insulator. Metal
conducts the heat away from your hands. Wood
does not conduct the heat away from your hands as
well as the metal, so the wood feels warmer than
the metal.
Convection
• Convection is the transfer of heat by the
motion of liquids and gases (FLUIDS).
– Convection in a gas occurs because gas expands
when heated and contract when cooled.
– Convection occurs because currents flow when
hot gas rises and cool gas sink.
– Convection in liquids also occurs because of
differences in density.
Water movement
Cools at the
surface
Cooler
water sinks
Convection
current
Hot water
rises
Weather
• When hot air rises, the air is replaced by the
surrounding cooler, more dense air, which we
feel as wind. Convection currents are
responsible for weather patterns in the
troposphere.
Sea Breezes
Earth’s climate due to convection
Cold air sinks
Where is the
freezer
compartment
put in a fridge?
It is put at the
top, because
cool air sinks,
so it cools the
food on the
way down.
Freezer
compartment
It is warmer
at the
bottom, so
this warmer
air rises and
a convection
current is
set up.
Radiation
• Radiation is the transfer of heat through
electromagnetic waves. Radiation DOES NOT
require matter in order to transfer thermal
energy!
Radiation
Main source of Earth’s radiation
?
There are no particles
between the Sun and the
Earth so thermal energy
CANNOT travel by
conduction or by
convection. ONLY....
RADIATION
Radiation
Shiny objects or light colored objects do not absorb
radiation as well as dull black objects.