Lesson 1 of 2
Energy and Systems
Define thermodynamic systems, boundaries, and forms of energy.
Systems and surroundings
In thermodynamics we analyze a system - the part of the universe we care about - separated from its surroundings by a boundary. Systems can be:
- Closed - no mass crosses the boundary (but energy can).
- Open - both mass and energy can cross (a control volume).
- Isolated - neither mass nor energy crosses.
Forms of energy
Energy shows up in many forms:
- Internal energy (U) - the microscopic energy of molecules.
- Kinetic energy - energy of motion.
- Potential energy - energy of position.
- Heat (Q) - energy transferred due to temperature difference.
- Work (W) - energy transferred by a force acting through a distance.
Why it matters
Correctly defining your system and identifying energy flows is the first step in every thermodynamics problem. Get this right and the equations follow naturally.