Air resistance, also called drag, acts upon a falling body by slowing the body down to the point where it stops accelerating, and it falls at a constant speed, known as the terminal velocity of a falling object. Air resistance depends on the cross-sectional area of the object, which is why the effect of air resistance on a large flat-surfaced object is much greater than on a small, stream-lined object.
Were it not for air resistance, all free-falling objects would fall at the same rate of acceleration, regardless of their mass. In a perfect vacuum, a feather and a bowling ball dropped from the same height strike the ground at the same time. This is true because acceleration is equal to force divided by mass. While the gravitational force upon the heavier bowling ball is greater than that upon the feather, the bowling ball's mass is also greater, offsetting the greater gravitational force. According to the Physician's Classroom, this rate of acceleration due to gravity is a constant 9.8 meters per second per second for all objects on Earth.
Air resistance is a type of friction due to collisions between the molecules of an object's leading edge and air molecules. Air resistance increases with surface area, but also with velocity, because a higher velocity means an object is displacing a greater volume of air per second. When the acceleration due to gravity is balanced by the force of air resistance, the falling object reaches terminal velocity, and does not fall any faster.