An object that is moving only because of the action of gravity is said to be free-falling and its motion is described by Newton's second law of motion.
​Newton's second law of motion: The second law states that the acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object.
The acceleration of the freely falling object is constant and equal to the acceleration due to gravity.
During free fall of the object, gravitational force acts on the body in a downward direction always and so the acceleration of the object remains in a vertically downward direction which is constant with time.
The most remarkable and unexpected fact about falling objects is that, if air resistance and friction are negligible, then in a given location all objects fall toward the center of Earth with the same constant acceleration, independent of their mass.
The force of gravity causes objects to fall toward the center of Earth. The acceleration of free-falling objects is therefore called the acceleration due to gravity.