Heat and Temperature

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Chapter 10

• Heat and Temperature

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Temperature

• In science, not based on HOT or COLD.
• Based on kinetic energy of particles in object.
• KE increases ? temp increases
• KE decreases ? temp decreases

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Thermometer

• Measure temp with thermometer.
• Different types for different tasks.
• Example
• In refrigerator ?Measures bending of metal
  strips.
• Digital ? Measures change in electricity.

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Temp. Scales

• Fahrenheit scale
• Units F
• Freezing Point 32F
• Boiling Point 212F
• Celsius scale
• Units C
• Freezing Point 0C
• Boiling Point 100C

• Kelvin scale
• Units Kelvin (K)
• Freezing Point 273 K (absolute zero)
• Boiling Point 373 K

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Conversions

• Celsius-Fahrenheit Conversion Equation
• Fahrenheit temp (9/5 x Celsius temp) 32
• F 9/5 C 32
• Fahrenheit-Celsius Conversion Equation
• Celsius temp 5/9 (Fahrenheit temp 32)
• C 5/9(F 32)
• Celsius-Kelvin Conversion Equation
• Kelvin temp Celsius temp 273
• K C 273

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Conversion Example

• Convert 57.8C to degrees Fahrenheit and in
  kelvins.
• F 9/5 C 32
• F 9/5 (57.8) 32
• F 104 32 136 F
• K C 273
• K 57.8 273 331 K

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Energy Transfer

• Sensation of temperature change is related to the
  energy transfer taking place.
• Holding ice cube in hand.
• Stepping into a hot bath.
• If neither feels warm or coldno energy transfer.
• Heat transfer of energy due to temperature
  differences b/w two objects.
• Greater difference in temp ? more energy transfer

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Methods of Energy Transfer

• Conduction involves direct
  contact of objects with unequal temperatures.
• Convection results from the movement of warm
  fluids itself (liquids gases).
• Radiation doesnt require contact of objects
  (electromagnetic waves) or movement of matter
  (can happen in a vacuum)

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Conductors

• Energy is transferred as heat quickly.
• Examples
• Metals Iron, copper, silver, etc
• Molten or liquid metals

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Insulators

• Slow the transfer of energy as heat.
• Examples
• Liquids
• Wood
• Rubber or Plastics
• Gases (Air)

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Specific Heat

• How much energy required to raise the temperature
  a certain degree.
• Determines if material good insulator or
  conductor.
• Smaller the specific heat ? better conductor
  (absorbs heat/energy easiest)
• Larger the specific heat ? better insulator
  (absorbs the least energy)

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Specific Heat Equation

• Energy (specific heat) x (mass) x (temp.
  change)
• H cm?T
• Specific heat units J/kgK or J/gC
• Water specific heat 4186 J/kgK
• 4.18 J/gC

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Example

• How much energy must be transferred as heat to
  the 420 kg of water in a bathtub in order to
  raise the waters temperature from 25C to 37C?
• H cm?T
• H 4186 J/kgK x 420 kg x 12 K
• H 21 000 000 J

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Law of Conservation of Energy

• Heat lost Heat gained
• Remember H cm?T
• cm?T cm?T
• cm(T1-T2) cm(T2-T1)
• metal water
• Example to come in class.

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Using Heat

• Heating and cooling of space is possible because
  of machines that transfer energy as heat from one
  place to another.

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Heating Systems

• Work can be done to increase the temp.
• Examples
• Human body energy from food ? transferred as
  heat to blood
• Central heat circulate heated fluids to each
  room
• Solar heat used by reptiles and solar
  collectors
• Usable energy in all energy
  transfers.

decreases
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Insulation

• Used to minimize energy transfers.
• R-value rating to measure the effectiveness of
  insulation materials.
• Greater the R-value ? greater the ability to
  decrease unwanted energy transfers.

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Cooling Systems

• Energy still transferred, BUT leaves the first
  substance with less energy and lower temp.
• Examples
• Liquid refrigerants uses evaporation to change
  into a gas (absorbs heat) and condenses back to a
  liquid (releases heat)
• Air conditioner uses process above convection
• Heat pumps can be used to cool or heat (reverse
  process)

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BACK
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BACK
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References

• Thermometer slide Pic http//puffernet.tripod.co
  m
• Temp Scales http//www.visionlearning.com/librar
  y/modules/mid48/Image/VLObject-318-021121021101.gi
  f
• Energy Transfer Pic http//apollo.lsc.vsc.edu/cl
  asses/met130/notes/chapter2/graphics/pan2.psd.gif
  
• Water Insulator Pic http//avstop.com/AC/apgener
  al/imageAQ3.JPG
• Snow Insulator Pic http//www.ukagriculture.com/
  Field_to_Fridge/images/wheatimage_januarylarge3.jp
  g
• Specific Heat Chart http//images.encarta.msn.co
  m/xrefmedia/aencmed/targets/illus/tab/T026242A.gif
  
• Molten Steel Pic http//www.nwpipe.com/images/pi
  c_molten.jpg
• Convection Pic http//www.stpaulmercantile.com/C
  onvection.gif
• R-values Pic physics.itsbaxter.com/thermal_insul
  ation.html
• Solar Heat Pic http//www.greenenergy.org.uk/sta
  /images/SWHsystem.gif
• Central Heat Pic http//www.diydata.com/planning
  /central_heating/vented.gif
• Air conditioner Pic http//home.howstuffworks.co
  m/ac.htm
• Refrigerator Pic http//www.energyquest.ca.gov/h
  ow_it_works/images/refrigerator.gif
• Anole Pic http//library.thinkquest.org/J0112365
  /reptile/graphics/green_anole.jpg
• Iguana Pic http//www.uvguide.co.uk/images/green
  iguana.jpg