NEB Class 11 • Physics • Study Guide

Gravitation Study Guide: NEB 11 Physics

Organise inverse-square force, field, potential and satellite equations into a derivation map, then use spaced questions and error analysis to make the knowledge transferable.

Diagnostic for concept, direction and algebra gaps
Seven-session sequence with derivation evidence
Simulation, retrieval schedule and exam checklist

Gravity bends inertial motion into an orbit.

Learn relationships

What the study guide adds to the concept chapter

The full Gravitation guide explains the physics and worked examples. This page turns it into a learning schedule. The CDC Grade 11 Physics page is the Nepal syllabus checkpoint.

The OpenStax institutional chapter stresses centre-to-centre distance, attraction and spherical symmetry. These are not decorative details: each controls the validity and direction of an answer.

Find the first weak decision

A 25-minute Gravitation diagnostic

Predict force change if one mass doubles and distance triples.
Distinguish G and g in words and SI units.
Draw the field direction due to one mass at four surrounding points.
Compare g at R and 2R from a planet centre.
Explain why V is negative when zero is at infinity.
Derive circular orbital speed from two force equations.
Explain why astronauts can feel weightless while gravity acts.

Mistake	Underlying gap	Repair
Uses surface gap as r	Geometry/model	Mark both centres before writing the law
Confuses G and g	Quantity meaning	Write name, definition and unit side by side
Adds potential as vector	Field/potential distinction	Draw field arrows; add potential numbers
Uses mgh for satellites	Approximation boundary	Compare h with Earth radius
Keeps satellite mass in v	Algebra/physical scaling	Cancel m before substitution

Concept hierarchy

The force–field–potential–orbit map

Force

F = GmM/r² is an attractive vector interaction between two masses.

Field

g = F/m = GM/r² is force per unit test mass at a point.

Potential

V = −GM/r is energy per unit mass and is scalar.

Orbit and escape

Radial force gives orbit speed; total-energy condition gives escape speed.

Review the Circular Motion study guide if radial equations are weak and the Work, Energy & Power study guide if energy-reference signs are unclear.

Seven focused sessions

A practical Gravitation learning sequence

Session	Focus	Active evidence
1	Universal law and scaling	Ten ratio predictions before calculations
2	Field and superposition	Direction diagrams and one zero-field comparison
3	Variation of g	Exact altitude relation and model for depth
4	Potential and potential energy	Sign explanations and two reference-level comparisons
5	Circular satellites	Derive speed, period and total energy
6	Escape speed and Kepler laws	Energy derivation plus scaling questions
7	Timed mixed retrieval	Unlabelled set, marked method and error repair

A 55-minute session can use ten minutes closed-book retrieval, ten minutes targeted explanation, thirty minutes problems and five minutes error logging. Mix at least one earlier topic into every later session.

Rebuild under pressure

Five derivations to practise from first principles

Surface field: equate mg with GMm/R² to obtain g = GM/R².
Altitude field: replace centre distance R with R+h.
Orbit speed: set GMm/r² = mv²/r and cancel satellite mass.
Orbit period: substitute v = 2πr/T into the orbit equation.
Escape speed: set final total energy at infinity to zero.

Do not memorise the last line alone. On a blank sheet, write the physical statement above each derivation: “gravity supplies inward acceleration” or “minimum escape has zero speed at infinity.” The statement tells you which equation begins the work.

Derivation check: orbit period

GMm/r² = mv²/r and v = 2πr/T. Substitution gives GM/r² = 4π²r/T², so T² = 4π²r³/(GM). Check: for the same central mass, a larger orbit has a longer period.

Make a prediction first

Institutional simulation activities

Use PhET Gravity Force Lab to test inverse-square scaling. Predict a ratio, change only one mass or distance, record the result, and explain it with F ∝ m₁m₂/r².

Then use PhET Gravity and Orbits. Predict force and velocity directions, change the central mass or initial speed, and relate the altered path to inertia plus inward acceleration. Avoid random clicking; every run should answer a written question.

Change	Prediction	Equation link
Double source mass	Force and field double	F, g ∝ M
Double separation	Force becomes one quarter	F ∝ 1/r²
Increase orbit speed	Path curvature changes	Required a_r = v²/r
Turn gravity off	Object follows tangent	Newton’s first law

Correct the cause

A Gravitation error log that improves transfer

Label each error as model, geometry, direction, quantity choice, algebra or interpretation. “Used distance above surface instead of centre distance” is geometry; “added potentials with arrows” is quantity choice; “said gravity is absent in orbit” is interpretation.

After one day

Redo the same concept with changed masses or radius.

After three days

Mix a force, field, potential and orbit question without headings.

After seven days

Derive orbit and escape formulas from verbal principles.

Explain aloud

Justify sign, direction and approximation before showing algebra.

Ratio questions are efficient retrieval: if r doubles, force and field quarter, potential magnitude halves, circular speed becomes 1/√2 and period becomes 2√2 times larger.

Keep the chapter active

A two-week consolidation schedule

Day	Task	Success evidence
1	Force and scaling set	All ratio predictions explained before calculation
3	Field versus potential comparison	Correct vector/scalar treatment
5	Altitude and depth models	Exact relation and assumptions stated
7	Orbit and escape derivations	Blank-page derivations without prompts
10	Mixed Mechanics set	Correct choice between force and energy methods
14	Timed retest	At least 80% and no repeated conceptual error

After each session, write one “because” sentence. Examples: “The satellite mass cancels because both gravitational and inertial terms are proportional to it,” or “Potential is negative because zero is chosen at infinity for an attractive field.” These sentences expose memorised results that lack a model.

Include one transfer prompt in every review: compare another planet, replace circular radius with a larger value, or ask what remains invariant. If the result changes in the wrong direction, use scaling before redoing arithmetic. This makes the study plan useful beyond familiar numbers. Keep the corrected response dated so the next review tests whether the same reasoning survives after a delay, not merely whether the page looks familiar.

Final checkpoint

Exam answer and readiness checklist

Distance is measured from the source centre.
Point-mass or spherical-symmetry assumption is stated where relevant.
Field directions are drawn; potentials are added as scalars.
The infinity reference explains the negative potential sign.
Satellite mass cancels from ideal orbit and escape speeds.
mgh is used only inside its near-surface approximation.
Final answer includes units and an inverse-square or energy check.

Readiness means you can derive orbit and escape results, explain weightlessness accurately and solve an unseen mixed set with at least 80% after delayed review. For online or physical NEB tuition, call 9846662070 with your diagnostic and error log.

Self-test

Ten retrieval prompts

State Newton’s gravitational law with direction and conditions.
Explain why centre distance matters.
Differentiate force, field, potential and potential energy.
Find the field ratio at r and 3r.
Write exact and small-height expressions for g.
Explain the uniform-density assumption for depth.
Derive circular orbital speed.
Derive orbit period and state its scaling.
Derive escape speed using total energy.
Explain apparent weightlessness in one precise paragraph.

Study tip: Answer in words first, then equations. If the verbal model is wrong, faster algebra only produces a faster wrong answer.

Frequently asked questions

Questions about studying Gravitation

What should I learn first in Gravitation?

Start with Newton’s inverse-square law, centre distance and vector direction, then build field, potential, orbit and escape ideas.

How can I remember the formulas?

Use a derivation map: force divided by test mass gives field; energy divided by mass gives potential; force gives orbit and energy gives escape.

Why do I confuse g and G?

They are different quantities. Write each full name, definition and unit whenever you start a study session.

How should I practise derivations?

Write the physical principle first, derive without notes, annotate assumptions and check the final scaling.

How often should I revise Gravitation?

Revisit errors after one, three and seven days, changing one variable or question form each time.

Where can I get help with NEB Gravitation?

For current online or physical tuition options, call 9846662070 and confirm timetable, class mode, teacher availability and fees.

References and next steps

Sources and related study guides

Use the Class 11 Physics revision roadmap to interleave Gravitation with earlier Mechanics topics. Scope and sources were checked on 2 August 2026. Follow current CDC, NEB and college instructions if requirements change.

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