It is a common assumption that heavier objects fall faster than lighter ones do. This is completely untrue. Every freely falling object, regardless of its mass, will accelerate at the same rate (9.8 meters per seconds squared near the surface of the Earth).
But why does this happen? After all, it is true that if object A has twice the mass of object B, gravity will pull twice as hard on object A. We can prove this by showing that object A has twice the weight of object B and, as you recall, weight is a measurement of how hard gravity pulls on an object. However, according to the law of inertia, the more mass an object has, the more force it will take to accelerate that object. Everyone knows it is much harder to push a 100 pound cart than it is to push a 50 pound cart. Therefore, even though gravity pulls harder on more massive objects, it needs every bit of this extra strength to be able to accelerate them at the same rate it accelerates smaller objects. This concept was proved by Galileo around the beginning of the 17th century. For more on Galileo see History Page 5.
However, you might still argue, doesn't a feather fall much more slowly than, say, a brick? But this just gets back into the topic of air resistance. A feather’s shape gives it a large amount of air resistance and this is what makes it fall slowly, not its low weight. A piece of paper for example, falls much more quickly when it is crumpled into a ball than when it is simply a flat sheet and here only its shape changes, not its weight. If you conducted the feather brick experiment on the Moon as one astronaut once did, you would find that both objects fall at the same rate because there is no air on the Moon to cause resistance.
