Centripetal force

Centripetal force is the net force directed toward the center of a circular path. It produces the inward acceleration required for circular motion.

Centripetal acceleration: The acceleration directed toward the center of a circular path, with magnitude equal to speed squared divided by radius. It is the inward acceleration that the net centripetal force produces.
Tension (physics): The pulling force transmitted through a taut string, rope, cable, or similar connector. String tension can point toward the center and keep an object moving in a circle.
Centrifugal force: An apparent outward force introduced when motion is described from a rotating reference frame. It contrasts with the inward net force measured in an inertial frame.
Acceleration: The rate at which velocity changes with time, including changes in speed or direction. Circular motion requires acceleration even when speed remains constant.
Newton's cannonball: A thought experiment in which a cannonball fired from a high mountain can orbit Earth if its speed is sufficient. It illustrates gravity continuously bending a projectile's path into an orbit.
Newton's second law: The principle that an object's net force equals its mass multiplied by its acceleration. Applying it radially gives the centripetal-force relation.
Gravitation: The mutual attraction between bodies with mass, described classically by Newton's law of universal gravitation. Gravity supplies the centripetal force for planets and satellites in orbit.
Inertial frame of reference: A reference frame in which an object with no net force moves at constant velocity. Centripetal force is defined as a real net force in this kind of frame.
Velocity: A vector quantity describing the rate and direction of an object's change in position. In circular motion its direction changes continuously, requiring an inward force.
Keplerian orbit: An idealized orbit governed by Newtonian gravity, following a conic section around a central body. For a circular Keplerian orbit, gravity supplies the required inward force.

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