Orbital mechanics concept check — a satellite continues moving in its orbit around Earth primarily because of which physical cause?

Difficulty: Easy

Correct Answer: Gravitational force

Explanation:


Introduction / Context:
In orbital mechanics, it is important to distinguish between the real physical forces acting on a satellite and the kinematic quantities used to describe its motion. A satellite stays in orbit because a central force continuously curves its trajectory, producing the required centripetal acceleration.


Given Data / Assumptions:

  • The satellite is in a stable, bound Earth orbit.
  • Earth's gravity is the dominant central force; atmospheric drag and other perturbations are neglected for this conceptual question.
  • Descriptions may use either inertial or rotating frames, but forces must be identified correctly.


Concept / Approach:

A body moving in a circular or elliptical path requires a centripetal acceleration directed toward the focus/center. This acceleration must be provided by a real force. For Earth satellites, that real force is the gravitational attraction between Earth and the satellite. “Centripetal” is not a separate force; it is the required inward acceleration. “Centrifugal” is a pseudo-force that appears only in a rotating (non-inertial) frame and is not the physical cause of orbital motion.


Step-by-Step Solution:

Recognize the satellite follows a curved path → requires inward (centripetal) acceleration.Identify the real physical interaction providing this: Earth–satellite gravitation.Conclude: gravitational force supplies the centripetal requirement that keeps the satellite in orbit.


Verification / Alternative check (if short method exists):

Set gravitational force equal to m * v^2 / r for a circular orbit: G * M * m / r^2 = m * v^2 / r → confirms gravity provides the centripetal requirement.


Why Other Options Are Wrong:

“Centripetal force” describes the role, not the source; “centrifugal force” is frame-dependent and not a real cause; “none” and solar radiation pressure are incorrect for sustained Earth orbits.


Common Pitfalls (misconceptions, mistakes):

Confusing centripetal acceleration with an independent new force; treating centrifugal force as real in an inertial frame.


Final Answer:

Gravitational force

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