what is heat ch 10.2 8th
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WHAT IS HEAT?
Chapter 10 Section 2
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Objectives:
Define heat as thermal energy transferred
between objects at different temperatures
Compare conduction, convection, and
radiation
Use specific heat capacity to calculate heat
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Section vocabulary:
Heat
Thermal energy
Thermal conduction
Thermal conductor Thermal insulator
Convection
Radiation
Specific heat
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Transferred Thermal Energy:
Heat: the energy transferred between objects
that are at different temperatures
Why do some objects feel hot and others
cold??
When 2 objects come in contact, heat istransferred from the highertemp to the lower
temp object
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Reaching the Same
Temperature:
Objects in contact, energy is transferred from
the warmer object to the colder object
When objects have the same temperature
there is no net change in thermal energy
One object may have more thermal energythan the other, both objects are at the same
temperature
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Energy Transfer:
http://resources.edb.gov.hk/cphysics/heat/tep/trans/heat_transfer.gif
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Conduction, Convection, &
Radiation:
3 Ways to transfer thermal energy:
http://4.bp.blogspot.com/_yHkXsgfstqE/Suzu5YuQkBI/AAAAAAAAAGM/0eorThn-bZA/s400/heat-transmittance-
means.jpg
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Conduction & Insulators:
Thermal conductors: substances that conduct
thermal energy very wellExample: doctors metal in a stethoscope
Thermal insulators: substance that do not
conduct thermal energy well
Example: doctors wooden tongue depressor
*Table in text pg. 283
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Convection:
Convection: the transfer of thermal energy by
the movement of a liquid or a gas
Circular patterns of convection due to
differences in density (convection currents)
Warmer water rises, cooler water sinks
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Convection:
http://upload.wikimedia.org/wikipedia/commons/0/08/Convection.gif
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Radiation: Radiation: the transfer of energy by
electromagnetic waves (ex: visible light, infraredwaves)
Energy transferbetween particles OR acrossempty space
Sun emits visible light you can see and infraredand UV waves you cannot see
Yourbody absorbs infrared waves which can befelt as heat
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Radiation:
http://www.wyckoffschools.org/eisenhower/teachers/chen/images/3-14.jpg http://www.valorfireplaces.com/_img/education/radiantheat.j
pg
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Radiation & the Greenhouse
Effect: The Earths atmosphere traps heat energy like
a greenhouse
Greenhouse gases: water vapor, carbon
dioxide, methane
Too many trapped gases may make the Earthtoo warm
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Heat & Temperature Change Thermal Conductivity: the rate at which a
substance conducts thermal energy
Example: Your seatbelt metal buckle has a
higher thermal conductivity; the cloth does notconduct heat well. They are both the same
temperature, the metal feels hotter!
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Specific Heat: Most metals have very low specific heat
Waterhas a very high specific heat
Substance Specific Heat(J/kgC)
Metal of seatbelt 500
Cloth of seatbelt 1,3
40Water 4,184
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Heat, Temperature, & Amount: Energy must be calculated, it cannot be
measured directly
Heat (amount of energy) is measured in joules
(J)
How much energy is needed to heat a cup of
water to make tea?
Must consider the waters mass, temperaturechan e, and specific heat
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Calculating Heat: Formula:
Heat (J) = specific heat (J/kgC) x mass (kg)
x
change in temperature (C)
You can now calculate the heat transferred to
the water
Heat increasing (positive value)
Heat decreasing (negative value)
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Quick Quiz: Heat is the transferbetween 2 objects with different
temperatures. (T/F)
Convection currents result from temperature differences
in liquids and gases (T/F)
Radiation is the means by which the energy from the
sun is transferred to the Earth (T/F)
Water stays warm or cool longer than land does
because water has a lower specific heat than land does
(T/F)