All objects, regardless of mass, will fall at the same rate. The heavy and light objects travel at the same rate because there are two competing factors that cancel each other out. The force of gravity is greater on the heavier object than on the lighter object, proportional to the object's mass. This means that an object with twice the mass will be pulled toward the earth with twice the force. On the other hand, the acceleration is proportional to the force divided by the mass. This means that an object that is twice the mass of another object will be accelerated twice as slowly as the lighter object given the same force. So in order for an object with twice the mass to move at the same rate as the lighter object, the heavier object must be submitted to twice the force. And this is exactly what the force of gravity does.