HEAT

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HEAT THERMAL ENERGY

• CH. 16

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State indicator

• 17. Demonstrate that thermal energy can be
  transferred by conduction, convection or
  radiation (e.g., through materials by the
  collision of particles, moving air masses or
  across empty space by forms of electromagnetic
  radiation).

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Heat flows spontaneously from hot objects to cold
objects

• Heat is also the transfer of thermal energy.

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What is Temperature?
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• Temperature is related to the average kinetic
  energy of an objects particles due to their
  random motion through space.

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Temperature

• The  reference point on the  Kelvin scale for temp
  erature  is absolute zero.
• 0 -273o C
• Absolute zero a temperature of 0K.  
• Room temp. would be 293o K
• The purpose for this is when we study gases,
  which have very low freezing points.

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Thermal energy depends on mass, temperature and
phase of an object.
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Thermal expansion occurs because particles of
matter tend to move farther apart as temperature
increases.
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• Gas expands more than liquids and solids

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Specific Heat

• The lower a materials specific heat is, the more
  its temperature will rise when energy is applied.
• Heat needed to raise the temp. of a 1g of an
  object 1 Celcius.

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Specific Heat

• Unique to every material
• The  lower an objects  specific heat, the more 
  the temp. increases  when heat is absorbed.
• Water has a large specific heat.
• Needs a lot of heat to change its temp

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Heat

• Heat  is measured in Joules or calories.
• One calorie is the energy the required to raise
  the temp. of 1g of water by 1oC.
• One calorie is equal to 1.184 J
• The unit for specific heat is J/g oC

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Q   m   c    ?T 

• Q heat
• M mass
• C specific heat (unique for the substance)
• ?T change in temperature

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• A calorimeter uses the principal that heat flows
  from hotter to colder objects until they both
  reach the same temperature.

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Heat and Thermodynamics

• Conduction in gases is slower than liquids
  solids because the particles collide less often
• Transfer of heat through direct contact is
  CONDUCTION

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Thermal  Conductors 

• Material  that conducts thermal  energy well.
  Examples copper aluminum pots pans wood
  vs. tile flooring

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Thermal  Insulators 

• Material  that conducts thermal  energy poorly.
• Examples air in a double pane window, wood,   
  fiberglass, fat

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Convection

• Transfer  of heat through moving 
  particles in fluids  (liquids  gases).
• Convection currents are important in many natural
  cycles.
• Convection Current occurs when a fluid circulates
  in a loop as it heats and cools. Example oven

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Radiation  

• Examples  Heat from the sun,  heat lamps used in 
  restaurants 
•   light colored object ?
•  Reflect heat 
•   dark colored object ?
•  Absorb heat

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The first law of thermodynamics

• ENERGY is CONSERVED!

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The 2nd Law of thermodynamics

• Heat can only flow from colder to hotter if work
  is done on the system.

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The 3rd Law of Thermodynamics

• Absolute Zero cannot be reached
• People are trying!
• Current record is down to about 90 picokelvin!
  Thats 9.0 x 10(-11)

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Temperature and Conductivity

• http//www.youtube.com/watch?vyXT012us9ng

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2 types of engines

• Internal combustion
• External combustion
• A  heat engine is any device that converts heat
  into work.
• Thermal  energy that is not  converted into work 
  is called waste heat.
• Waste  heat is lost to  the environment. 

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Internal combustion engine
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External combustion engine
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Most heating systems are convection to distribute
thermal energy
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• Heat pumps must do work on a refrigerant in order
  to reverse the flow of thermal energy

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Alternate home heating is part of our energy
future!