centripetal acceleration

Meaning: Centripetal acceleration is the acceleration of an object moving on a circular path. It points toward the center, perpendicular to the velocity, so it changes direction but not speed; it exists even at constant speed because velocity is a vector. The net inward force causing it, the centripetal force, is not a new kind of force: tension, gravity, friction, or a normal force supplies it.

Equation: ac = v²/r = ω²r, where ac is centripetal acceleration (m/s²), v is speed (m/s), r is radius (m), and ω is angular speed (rad/s). Fc = mac = mv²/r, with Fc in N and m in kg.

On the MCAT: Expect cars on curves, satellites, centrifuges, or a mass on a string. Doubling v quadruples ac; doubling r at constant v halves it. On a flat curve friction supplies the force, so μmg = mv²/r and the maximum speed does not depend on mass. In a circular orbit, gravity supplies it.

Common confusion: In an inertial frame, no outward force acts on the object. If the string breaks, inertia carries the object along the tangent, not outward. Do not draw centripetal force as an extra force on a free-body diagram.