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:
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:
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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