A centripetal force is the inward resultant force needed for circular motion. Newton's second law and centripetal acceleration give magnitude for a particle of mass , speed , and path radius . It is a role played by an actual interaction, such as tension or an electric force, rather than an additional interaction to add to a free-body diagram. A purely radial centripetal force is perpendicular to the velocity, so it does no work and leaves the speed unchanged.
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Centripetal force is the force that acts on an object moving in a circular path, directed towards the center of the circle around which the object is moving. It is the force that keeps the object from flying off in a straight line due to its inertia. The term "centripetal" comes from Latin, meaning "center-seeking.