Orbits as gravitational motion
An orbiting body can remain in continuous gravitational free fall.
Key knowledge
An orbiting satellite moves under gravity while its sideways motion can keep it from reaching the surface. In the Newtonian two-body model with inverse-square attraction, a bound non-radial relative orbit is an ellipse. Such an orbit does not require continuous rocket thrust.
Conditions and scope
- The ellipse statement assumes point masses, or the exterior field of a spherical central mass, and nonzero orbital angular momentum.
- It excludes atmospheric drag, other bodies, non-spherical gravity, thrust and relativistic corrections; real orbits can change.
Sources · 3
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
- Basics of Space Flight, Chapter 3: Gravity & Mechanics — How Orbits WorkNASA Jet Propulsion LaboratoryTeaching resource
- University Physics Volume 1, 13.5: Kepler's Laws of Planetary MotionOpenStax, Rice UniversityTextbook chapter
- Gravitation · Physics (2026–27 reprint)National Council of Educational Research and Training (NCERT)Textbook chapter · PDF
Evidence and review
NASA/JPL's free-fall account and the textbook's Newtonian inverse-square two-body orbital model; no trajectory was newly calculated.
2026-10-10 · English free-fall and bound-orbit scope checked against NASA/JPL and University Physics section 13.5; radial motion and general potentials are excluded.
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
Scope or convention differs
Planetary elliptical-orbit teaching and satellite free fall.
This comparison does not independently derive the general two-body ellipse or its sideways-motion conditions.
National Council of Educational Research and Training (NCERT)
- Gravitation · Physics (2026–27 reprint) IndiaEnglish
§7.2, printed p128: planetary ellipses; Points to ponder, printed p141, point4: satellite free fall
- Gravitation · Physics (2026–27 reprint)
Entry details
Permanent link to this entry ↗- Record identity
- cosmos-orbital-motion
- Revision
- core.1
- Structured reference record
- Essential core · first collection