Circular motion in which the object moves with constant speed . The length of time needed for one complete cycle of any kind of periodic motion. In the case of circular motion period is the time needed for the moving object to complete one circle. This is also called radial acceleration since it is along the radius.
Apparent weightlessness is the weightlessness felt in the shuttle.
Instead, the feeling of weightlessness is due to the fact that the shuttle is accelerating toward the earth at a rate equal to gravity at the height of the orbit. The acceleration of an object is directly proportional to the net force acting on the object and the direction of the acceleration is in the direction of the applied net force. In circular motion the acceleration is directed toward the center of the circle and so is the net force. Every particle in the universe attracts every other particle with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them. This force acts along the line joining the two particles.