Learning objective
- Describe the differences between extensive and intensive quantities, state and path quantities, steady state and unsteady systems.
- Describe the requirement for a system boundaries
- Recall the six-term version of UAE
- Simplify and use UAE for various type of system.
System
A system contains anything that interacts with each other. The boundary of a system is determined by you.
Rules for defining systems
- Do not change the system in the middle of your calculations
- System boundaries can be any shape, but they must be a closed surface (meaning they must be containing something but not open to more and more things).
- System boundaries can be rigid or flexible.
Types of system
- Closed: mass cannot pass the boundaries, but energy can
- Open: mass can pass
- Non-isolated: things can pass
- Isolated: nothing can pass, even mass or energy
- Homogeneous: properties are the same
- Non-homogeneous: properties varies
- Steady: system stage is constant over time
- Unsteady: system state changes
Intensive and extensive quantities
- Intensive Quantities: do not change on scale
- Pressure
- Color
- Temperature
- Melting point, etc.
- Extensive Quantities: depend on scale
- Mass
- Moles
- Area
- Volume, etc. Intensive quantities cannot be counted, while extensive quantities can be counted. Derived Quantities: quantities that are a combination of extensive quantities.
- Density = mass/volume
- Treat them like intensive quantities
State and Path Quantities
State quantities are independent of path. Path quantities are dependent.
Conservative and Non-conservative Forces
- Conservative force: independent of the path taken
- Example: gravitational, spring force, magnetic and electric force, etc.
- Non-conservative: dependent of the path taken
- Example: Friction, Air drag, etc.
UAE: Universal Accounting Equation
Final amount - Initial amount = input - output + generation - consumption