Centripetal force is the net force that acts on an object, directed inward toward the center of a circular path, necessary to keep the object moving in a circular trajectory. This force is responsible for continuously changing the direction of motion of an object, even if the speed remains constant, and is always perpendicular to the object's instantaneous velocity. Mathematically, the magnitude of this force is determined by the mass of the object and the square of its orbital velocity, divided by the radius of the circular path. The requirement for this inward force means that any object moving in a perfect circle must be acted upon by a centripetal force; if this force drops to zero, the object will follow a path tangent to the circle, following principles of inertia.