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Convection Powered By Docstoc
					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

• 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
• 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


• The transfer of energy through
  empty space or a gas medium
  is called radiation.

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

• For example, radiation enables
  sunlight to warm Earth’s

• 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.
• The transfer of heat by the movement of a
  heated fluid (liquid or gas) is called

• 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
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
   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
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
   substances to spread farther
3. But the molecules of wax
   spread apart much more
   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

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

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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