Bellringer
What two SPECIFIC pieces of evidence to
geologists study to determine the interior of our
planet?
Convection and the
Mantle
Notes
Types of Heat
Transfer
• When an object heats up, particles in
the object have more energy and move
faster. The energy can travel, or
transfer from a warmer object to a
cooler object.
• Energy NEVER transfers from cooler to
warmer.
Slower
Faster
Types of Heat
Transfer
• Radiation is the transfer of energy
through space. For example, sunlight
travels through space by radiation and
warms Earth’s surface. Radiation also
explains why your hands get warm
when you hold them near a fire.
• Radiation DOES NOT require a
medium to transfer its energy.
Types of Heat
Transfer
• Conduction is the transfer of heat
between objects that are touching. If
you touch a hot pot, heat travels from
the pot to your hand by conduction.
Types of Heat
Transfer
• Convection is the transfer of heat by
the circular motion of particles in a fluid
(gas, liquid, plastic solid). Moving
particles transfer heat throughout the
fluid.
• This is where the phrase, “warm air
rises,” is applicable. BUT it needs to be
rephrased to state, “warmer air rises,
cooler air sinks.”
http://www.thisoldearth.net/Images/Convection2.gif
Convection Currents
• The movement of particles due to the
transfer of energy by convection is
known as a convection current.
• Multiple current can occur within a
single fluid. ONE current is known as a
convection cell.
Convection Currents
• A convection current starts when there
are differences in temperature and
density of a fluid. Density is the amount
of mass in a given volume of a
substance (how tightly packed the
particles are). A high-density substance
feels heavy for its size.
• soccer ball vs. bowling ball
Convection Currents
• Which is less dense: hot air or cold air?
• Which is less dense: hot air or warm
air?
• Because particles move faster when
they are warmed up, they also tend to
spread out, therefore the warmer a fluid
becomes, the less dense it will become
as well.
Convection Currents
• Suppose you put a pot of soup on the
stove. The soup at the bottom of the pot
will get warm first. Because it is warmer,
the soup at the bottom of the pot is less
dense than the cooler soup above it. So
the warmer soup rises. At the same
time, the cooler, denser soup sinks to
the bottom of the pot.
Convection Currents
• The cooler soup now at the bottom gets warmer,
and the process repeats. A constant flow of
particles begins. Warmer soup keeps rising, and
cooler soup keeps sinking. This movement of
particles transfers heat throughout the soup.
• This is the same process that occurs with cooling
houses from the ceiling and heating them from
the floor.
Convection Currents
in Earth
• The heat inside Earth causes
convection currents in the mantle and
outer core.
• Convection currents inside Earth are
like convection currents in a pot a soup.
Hot materials rise to the top, and cooler
materials sink to the bottom.
Convection Currents
in Earth
• Convection currents in the mantle move
very slowly. This is because the mantle
is made of solid rock.
• Remember, Earth is like a giant magnet
because of currents in the outer core.
Those currents are convection currents.