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• Temperature


  The quantity we measure with a thermometer

  
• Heat transfer


  The movement of energy from one place or material to another as a result of a difference in temperature
• Thermal equilibrium


  Two objects are in thermal equilibrium if they are in close contact that allows either to gain energy from the other, but nevertheless, no net energy is transferred between them
• Temperature scales


  • Celsius
  • Fahrenheit
  • Kelvin

  
• Temperature conversions


  1. Celsius to Fahrenheit

  2. Celsius to Kelvin

  
• Constant-volume gas thermometer


  The pressure of the gas is a thermometric property
• Thermal expansion


  • Expansion of materials when heated
  • Contraction of materials when cooled

  
• Thermal expansion coefficients


  • Steel
  • Copper
  • Aluminum
  • Glass
  • Concrete
• Bimetallic strip


  Curvature depends on temperature
• Calculating linear thermal expansion

  Use thermal expansion coefficient and temperature change

  
• Thermal expansion in 2D and 3D


  Expansion in all directions, not just linear

  
• Density of water as a function of temperature

  
• Calculating thermal expansion of a gasoline tank

  Use thermal expansion coefficient and temperature change
• Calculating thermal stress in concrete blocks

  Use Young's modulus and temperature change
• Mechanical equivalent of heat

  Work needed to produce the same effects as heat transfer, 1 kcal = 4186 J
• Temperature change and heat capacity


  Q = mc∆T, where c is the specific heat capacity
• Specific heat capacity depends on temperature
• Calorimetry


  Use of a calorimeter to measure heat or specific heat capacity
• Phase diagram of water
• Dry ice sublimation and frost formation
• Phase change and latent heat

  Heat added during melting or boiling does not change the temperature until the transition is complete
• Phase diagram of water

  • Melting-point curve has a negative slope, showing that you can melt ice by increasing the pressure

  
• Direct transitions between solid and vapor

  • Dry ice sublimes directly to carbon dioxide gas
  • Frost forms patterns on a very cold window, an example of a solid formed directly from a vapor

  
• Direct transitions between solid and vapor are common, sometimes useful, and even beautiful
• Where does the heat added during melting or boiling go, considering that the temperature does not change until the transition is complete?
• Heat of fusion


  The energy per unit mass required to change a substance from the solid phase to the liquid phase, or released when the substance changes from liquid to solid
• Heat of vaporization


  The energy per unit mass required to change a substance from the liquid phase to the vapor phase
• The heat Q absorbed or released in a phase change in a sample of mass m is given by Q = mL, where the latent heat of fusion Lf and latent heat of vaporization Lv are material constants that are determined experimentally
• Calculating Final Temperature from Phase Change

  1. Three ice cubes are used to chill a soda at 20°C with mass msoda=0.25kg

  2. The ice is at 0°C and each ice cube has a mass of 6.0 g

  3. Assume that the soda is kept in a foam container so that heat loss can be ignored, and that the soda has the same specific heat as water

  4. Find the final temperature when all ice has melted
• Mechanisms of Heat Transfer

  • Conduction
  • Convection
  • Radiation
• Conduction


  Heat transfer through stationary matter by physical contact
• Heat transferred from the burner of a stove through the bottom of a pan to food in the pan is transferred by conduction
• Convection


  Heat transfer by the macroscopic movement of a fluid
• Convection takes place in a forced-air furnace and in weather systems
• Radiation


  Heat transfer by the emission or absorption of electromagnetic radiation
• An obvious example is the warming of Earth by the Sun. A less obvious example is thermal radiation from the human body
• Conduction


  • Insulation is used to limit the conduction of heat from the inside to the outside (in winter) and from the outside to the inside (in summer)
  • Molecules in two bodies at different temperatures have different average kinetic energies
  • Collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions
• Calculating Heat Transfer through Conduction

  1. A polystyrene foam icebox has a total area of 0.950 m^2 and walls with an average thickness of 2.50 cm

  2. The box contains ice, water, and canned beverages at 0°C

  3. The inside of the box is kept cold by melting ice

  4. How much ice melts in one day if the icebox is kept in the trunk of a car at 35.0ºC?
• Convection


  • Air heated by a gravity furnace expands and rises, forming a convective loop that transfers energy to other parts of the room
  • Natural convection plays an important role in heat transfer inside a pot of water
• Fur is filled with air, breaking it up into many small pockets. Convection is very slow here, because the loops are so small. The low conductivity of air makes fur a very good lightweight insulator