Physics

• Vacuum flasks


  Able to keep liquids in its initial temperature for a very long time
• Vacuum flasks

  • Have a sealed lid that secures the liquid inside the container and prevents leakage
  • Designed with a double-walled silvered surface with a vacuum
• The silver surface inside the bottle prevents heat transfer due to radiation since silver is an excellent reflector and has low emissivity
• Thermos flask

  Example of a thermodynamic system
• Laws of thermodynamics


  Deal with understanding the evolution of heat and its effects on thermodynamic systems
• Thermodynamic system


  Any object or collection of objects with a capacity for energy transfer
• System


  The object or collection of objects being studied
• Wall/Boundary


  Separates the system from its surroundings
• Surroundings


  Everything else outside the system
• Open system


  • Can exchange both energy and matter with its surroundings
• Open system

  • Fish and pan when frying a fish
• Closed system


  • Can exchange energy with its surroundings, but its wall does not permit the exchange of matter
• Isolated system


  • Does not interact with its surroundings since its wall is impermeable to both energy and matter
  • Thermodynamic states are constant over time
• Isolated system


  • Ideal thermos
• Diathermal boundary


  Allows heat transfer, can be used to create open or closed systems
• Adiabatic boundary


  Does not allow heat transfer, used for isolated systems
• Always identify the thermodynamic system, its boundary, and its surroundings before analyzing any thermodynamic process
• A thermodynamic system has a potential to exchange energy with its surroundings
• The boundary separates the system and the surroundings
• The system, its boundary, and its surroundings make up a thermodynamic universe
• Softdrinks in a styrofoam box

  • Closed system
• Helium gas in a balloon

  • Open system
• Barbeque on an open grill

  • Open system
• Liquid mercury in a thermometer

  • Closed system
• Clothes drying under the sun

  • Open system
• A thermodynamic universe consists of the thermodynamic system, its boundary, and its surroundings
• A thermodynamic system has the potential to exchange energy with its surroundings through a boundary
• A system is open if it allows both energy and matter exchange, closed if it allows energy exchange but not matter, and isolated if it does not allow energy and matter exchange
• A diathermal boundary allows energy transfer while an adiabatic boundary does not
• First Law of Thermodynamics

  Heat flows whenever there is a change in temperature. We use thermal energy in a lot of ways and you have already learned how heat is transferred and changed to other forms of energy.
• Mechanical turbines and other engines all operate using the concept of the first law of thermodynamics.
• First Law of Thermodynamics

  The change in internal energy of a system is equal to the quantity of the thermal energy and work done on the system.
• First Law of Thermodynamics

  1. State the relationship between changes internal energy, work done, and thermal energy supplied

  2. Solve problems involving the application of the First Law of Thermodynamics in contexts such as, but not limited to, the boiling of water, cooling a room with an air conditioner, diesel engines, and gases in containers with pistons
• Thermodynamics


  The branch of physics that deals with the transfer of thermal energy. It also deals with heat and work.
• Heat


  The transfer of energy from a system to the environment
• Work

  The transfer of energy into mechanical means
• The first law of thermodynamics deals with thermal energy, internal energy, and work.
• Conditions that determine whether Q or W must be positive

  • Q is positive if the heat is added to the system
  • W is positive if work is done by the system
  • Q is negative if the heat leaves the system
  • W is negative if work is done on the system
• The first law of thermodynamics explains that as long as there is a transfer of energy on the system, there will be changes in the thermal energy of the system.
• When W and Q are greater than zero, then energy is added to the system, but if W and Q are less than zero, then energy is removed from the system.