Objects fall at the same velocity regardless of their weight, if gravity is the only force acting upon them. In a vacuum, where air resistance has been eliminated, a bowling ball and a feather fall at the same speed.
A falling object accelerates at a constant rate due to the gravitational force of the earth. If there were no air resistance, an object would continue accelerating at the same rate until it hits the ground. However, the presence of air means the object is constantly colliding with countless air molecules. These accumulated collisions create resistance, and gradually slow the falling object until it reaches the point where the force of gravity and the force of air resistance are equal. At this point the object falls at a constant speed which is known as the "terminal velocity."