# Convection

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```					Heat Transfer
Lava Lamp
• A lava lamp consists of an enclosed container
with two substances of different densities. One
substance is wax and the other is a less dense
oil.

• Using heat from a light-bulb in the bottom of the
lamp, the oil and wax are heated up.
Opening questions
• Can you explain the motion of the wax in the
lava lamp over time?

• Explain what happens to the energy of the lamp
over time?
Connection to Earth Science
(Geology)
• Energy moves through the earth

• Either its transported or transferred
Heat transfer
• Occurs when thermal energy is transferred
from a warmer object to a cooler object
Types of heat transfer

Conduction

Convection.
• The transfer of energy through
empty space or a gas medium

• no direct contact between a
heat source and an object.

sunlight to warm Earth’s
surface.
Conduction

• Heat transfer by direct contact of particles of
solid or liquid matter is called conduction.

• The energy moves but the medium does not

• An example is when a spoon heats up in a
hot pot of soup.
Convection
• The transfer of heat by the movement of a
heated fluid (liquid or gas) is called
convection.

• The medium moves to transport the
heat from one place to another
The oil and wax movement in a
lava lamp is an example of
convection
Convection
1. Gain heat, Faster atoms, spread out
2. Greater volume for same mass =
less dense
3. Rise up, and lose heat to other objects
4. Pushed to side by newer, hotter material
5. Cools, loses heat, more dense, sinks
Examples of convection
Convection example
• An example of convection occurs in
heating a pot of soup on a stove.
Convection Current
• Is the flow of less dense hot material
upwards and more dense colder material
outward and downward

• Convection cycle or cell is one loop of a
convection current
Convection in the earth
Results of convection
• Heat added to lithosphere may melt the rock,
forming magma that flows from volcanoes

• There is a current created in the Asthenosphere
causing rotation in the mat .

• The crust and lithosphere also undergo pressure
to move
Difference in motion
• Astenosphere bends and slides

• Crust/lithosphere breaks and is carried
along
Steps to convection in a pot
1. As soup at the bottom of the pot gets hot,
it expands and becomes less dense.
2. The warm, less dense soup moves
upward, floating over cooler, denser
soup.
3. At the surface, the warm soup spreads
out and cools, becoming denser.
4. Then gravity pulls this cooler, denser
soup down to the bottom, where it is
heated again and begins to rise.
Heated lava lamp
1. When the lamp is turned on,
both the wax and the oil
absorb energy.
2. This causes the individual
molecules of both
apart.
3. But the molecules of wax
than the molecules of oil do
Density and heat
1.   In eighth grade, you learned that the density of a substance
changes when it absorbs energy.

2.   As the molecules get more energy, they vibrate faster and
farther, decreasing the density.

3.   We imagined the molecules to be connected by little
springs. When the substance absorbs energy, the “springs”
stretch a little farther, increasing the volume of the material.

4.   It has no effect on the mass of the material or the size
of the individual molecules, only on the size of the
sample.

5.   If the volume of the sample increases and the mass does
not, the density will decrease.
Convection is the engine of the
Earth
1. Heat from deep inside the Earth rises
through conduction to the top of the
mantle.

2. The material at the bottom of the
Astenosphere begins to move upward
as it becomes less dense this creates an
area of upwelling
Convection cycle continued
3. As the heated material rises to the top of the
layer it transfers its heat to the lithosphere/crust
and begins to cool, and becomes denser again

4. The cooler material is pushed to the side by
hotter material beneath

5. The cooler material sinks towards the bottom of
the layer over time

6. Cycle repeated

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 views: 5 posted: 2/10/2012 language: pages: 23