Systems and boundaries
Choose what belongs to an investigation, describe its condition at a stated time, and identify interactions with what lies outside its boundary.
Key knowledge
Describing a system requires identifying its components and interactions, its boundary, and relevant inputs and outputs. What counts as internal or external depends on that chosen boundary.
Conditions and scope
- A boundary is part of the model and must be stated before applying a balance law.
Sources · 13
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Massachusetts Institute of Technology2 sources
- Lectures on Thermodynamics, Chapter 1: Energy Accounting, Variables and Properties of SystemsGerbrand Ceder · Massachusetts Institute of TechnologyCourse notes · PDF
- MIT Unified Engineering Thermodynamics — State, heat and workIan A. Waitz (course instructor) · Massachusetts Institute of TechnologyCourse notesUnified Engineering Thermodynamics, Chapter 2: Thermodynamics ConceptsUnified Engineering Thermodynamics, Chapter 3: Changing the State of a System with Heat and Work
- NPTEL Advanced Engineering Thermodynamics — Systems and exchange classificationP. Mahanta · Indian Institute of Technology Guwahati / NPTELCourse notesAdvanced Engineering Thermodynamics, Module 1: Classical Thermodynamics, Lecture 1: Review of Thermodynamics — Concepts of classical thermodynamicsAdvanced Engineering Thermodynamics, Module 1: Classical Thermodynamics, Lecture 1: Review of Thermodynamics — System approach and classification of system
- University Physics Volume 1, 3.1 Position, Displacement, and Average VelocityWilliam Moebs, Samuel J. Ling, Jeff Sanny · OpenStax / Rice UniversityTextbook chapter
- Introduction to Engineering Thermodynamics — Systems, state and boundary heatClaire Yu Yan · University of British Columbia Okanagan / BCcampusTextbook chapterIntroduction to Engineering Thermodynamics, 1.2 System and surroundingsIntroduction to Engineering Thermodynamics, 1.4 State, process, and cycleIntroduction to Engineering Thermodynamics, 4.2 Heat transfer across a boundary
- NGSS Appendix G: Crosscutting Concepts (2013)NGSS Lead States — Next Generation Science StandardsTeaching resource · PDF
- University Physics, volume 1: Newton's Second LawSamuel J. Ling, Jeff Sanny and William Moebs / OpenStax, Rice UniversityTextbook chapter
- Systems and conservation of momentum · Physical Sciences 12SiyavulaTextbook chapter
- Basic Thermodynamics · Module1K. Srinivasan and Pradip Dutta · IIScCourse notes · PDF
Evidence and review
NGSS Appendix G, systems and system models; OpenStax 5.3, internal and external forces.
2026-10-10 · System-boundary convention only; no claim that a selected boundary makes a system isolated.
Foundational review
2026-10-10 · Fresh primary-source inspection of the complete compact record, including every statement, equation, quantity and material condition, followed by independent AI editorial review. This check does not certify all linked lessons or every passage of every cited publication.
Sources from other places
Agreement within this scope
Choosing a system boundary determines which components, interactions and transfers count as internal or external.
A boundary is chosen for the problem; matter and energy exchanges then belong in the system description.
Siyavula
- Systems and conservation of momentum · Physical Sciences 12 South AfricaEnglish
2.4 Systems, ESCJD; internal and external forces
- Systems and conservation of momentum · Physical Sciences 12
Indian Institute of Science · NPTEL
- Basic Thermodynamics · Module1 IndiaEnglish
System, surroundings, boundary; slides7–11
- Basic Thermodynamics · Module1
Related articles
Physical systems, states, boundaries, and environments ↗Entry details
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