How does Heat Energy

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How does Heat Energy transfer from one substance
to another?
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If you put a hot cup of coffee into a
refrigerator, would cold transfer from the
fridge to the coffee, or would hot transfer
from the coffee to the fridge?
Hmmmm.
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Here is how it works

• Heat Energy is what makes the coffee hot.
• Since the inside of refrigerator has a lower
  temperature than the coffee, heat energy travels
  from the coffee to the refrigerator, following
  the temperature gradient.
• The temperature gradient is kind of like the
  slope of a hill --- the steeper the hill, the
  faster a ball will roll down it.
• In a similar way, heat will leave the coffee
  faster in the beginning and at a slower and
  slower rate as the coffee cools.

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ENERGY FROM THE SUN

• 1. The SUN is the SOURCE of most of the Earth's
  SURFACE HEAT.
• 2. HEAT is TRANSFERRED as a result of a
  Difference in TEMPERATURE.
• 3. HEAT received from the SUN is transferred to
  different parts of Our Planet.
• 4. The SUN produces HEAT and LIGHT WAVES, which
  are a small part of the ELECTROMAGNETIC
  SPECTRUM.  The Spectrum includes all ENERGY
  Forms, such as LONG RADIO WAVES, SHORTER X-RAYS,
  AND ULTRAVIOLET WAVES.
• 5. The ATMOSPHERE REFLECTS some ENERGY WAVES that
  reach Earth BACK into SPACE.  The ATMOSPHERE
  ABSORBS some ENERGY.  LAND AND WATER SURFACES
  ABSORB ENERGY that reaches the Earth's surface.

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ENERGY FROM THE SUN

• 6. POLAR ICE Reflects the Sun's ENERGY and
  absorbs LITTLE of it.  WATER also Reflects SOLAR
  ENERGY, especially when the Sun is near the
  Horizon.  SAND and SNOW are other materials that
  tend to reflect SOLAR ENERGY.
• 7. VEGETATION, DARK ROCKS, AND BLACK SURFACES,
  such as ASPHALT Absorb LARGE amounts of SOLAR
  ENERGY.  The ENERGY is then RETURNED to the
  Atmosphere as INFRARED RADIATION and HEAT.
• 8. WATER VAPOR and CARBON DIOXIDE in the Air
  absorb some of these INFRARED WAVES, and some of
  them are RE-EMITTED to Earth.  This absorbed
  INFRARED ENERGY keeps HEAT in the TROPOSPHERE. 
  The WARMING EFFECT is called THE GREENHOUSE
  EFFECT.
• 9. Earth's SURFACE and ATMOSPHERE LOSE HEAT when
  they are not FACING the SUN.  LAND areas LOSE
  HEAT QUICKLY.  WATER LOSES HEAT MORE SLOWLY. 
  Earth would have Great differences in DAY and
  NIGHT TEMPERATURES if it were not for the
  ATMOSPHERE, which TRAPS HEAT and constantly moves
  it from one place to another.

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Copy all
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Now that we know which way heat energy travels
(from hot to cold), how does it actually travel?

• There are three types of heat transfer
• CONDUCTION
• CONVECTION
• RADIATION

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Conduction

• Conduction is transfer through direct contact.
• On a molecular level, hotter molecules are
  vibrating faster than cooler ones.
• When they come in contact, the faster moving
  molecules bump into the slower moving molecules
  and heat is transferred!
• This is how heat is transferred to your finger if
  you touch a hot stove!?

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Convection

• When fluids are heated, currents are created.
• This is because the individual molecules that
  come in contact with a hot surface expand, become
  less dense, and rise.
• Steps in the convection cycle heat, rise, cool,
  and sink
• When this happens, other molecules circulate down
  and take their place, and a cycle is established.
• An example of this can be observed in the air
  currents that are created in a room with a
  radiator against one wall.
• The air in contact with the radiator rises, moves
  across the ceiling to the far wall, sinks, and
  then comes back to the radiator across the floor.

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Radiation

• Radiated heat energy travels as an
  electromagnetic wave.
• Comes from the sun.
• Electromagnetic waves travel at the speed of
  light, which is 300,000,000 meters per second.
• Sometimes these waves are in the visible part of
  the spectrum, like when something is red hot.
  You can see how hot it is, but you can also feel
  it from a distance, as your skin absorbs the
  energy.
• Question Do you think that radiated heat needs
  a medium to travel through like heat transferred
  by convection does?

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NO!

• Electromagnetic waves do not need a medium to
  travel through, although they can travel through
  many substances.
• If this wasnt true, we wouldnt feel the heat of
  the Sun here on Earth!

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Q.) When you put a teapot on the stove to boil
water, which of the three kinds of heat transfer
can be observed?
A.) Actually, all three!

• First, there is conduction between the burner and
  the teapot, and then conduction between the
  teapot and the water molecules that are in direct
  contact with the teapot.
• Next, there is convection in the water as the
  heated molecules of water from the bottom of the
  teapot rise and spread their heat energy to the
  cooler molecules above them through direct
  contact. This convection current also pushes
  cooler molecules of water down to the bottom
  where they come in contact with the heated bottom
  of the teapot.
• While all of this is occurring, heat energy is
  being radiated in all directions from the from
  the burner and is absorbed by other objects. You
  can feel this energy if you stand too close!

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Conduction, Convection and Radiation
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Conclusion

• When objects are in contact this transfers heat
  by conduction. Liquids and gases can move high or
  low energy molecules to another region through
  convection. Atoms can radiate energy that can
  energize a distant atom, resulting in heat
  transfer by radiation.14

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The End