Nano PHYSICS . MECHANICS . DYNAMICS . FORCES AND INTERACTIONS

System vs Surroundings

Choose the object or collection of objects you will analyze, identify what lies outside it, and decide which forces are external to that chosen system.

Physics · Mechanics · Dynamics · Forces and Interactions · System vs Surroundings
Access for this nano-lesson
Unsigned visitors can show & copy prompts for Steps 1-3. Signed-in free accounts can also Run with AI for Steps 1-2. Paid accounts unlock everything (Steps 1-6 + Help prompts + AI).
Steps 1-3 Free Steps 4-6 Paid
STEP 1
Orient: draw a boundary around the system
Free
Learn what a system is in mechanics, what counts as surroundings, and why the same physical scene can be modeled using more than one valid system.
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Goal: define a system boundary before classifying any force as internal or external.
STEP 2
Conceptual grounding: single-object and multi-object systems
Free
Compare what changes when you analyze one object versus a collection of interacting objects.
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Goal: explain why internal and external force labels depend on the chosen system boundary.
STEP 3
Real-world connection: choose the system that answers the question
Free
See how a useful system choice changes from problem to problem, even when the same objects are present.
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Goal: select a system that matches the quantity or motion the problem asks you to study.
STEP 4
Check your understanding: system-boundary mini-quiz
Paid
Attempt each question before revealing the reasoning about systems, surroundings, and force classification.
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Goal: identify a stated system and classify interactions relative to its boundary.
STEP 5
Practice: classify forces across system boundaries
Paid
Work through increasingly rich scenes by defining a system, naming its surroundings, and classifying forces relative to the boundary.
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Goal: make the system boundary an automatic first step in force and interaction analysis.
STEP 6
Summary & reflection + system-boundary explorations
Paid
Consolidate the system-surroundings method and explore how models change when you redraw the boundary.
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🔒 ▶ Explore interactive simulation
Goal: build the habit of naming a system explicitly before classifying forces or applying a mechanics principle.