Here on earth we are so used to seeing heavier objects fall faster than lighter objects; if I were to drop a bowling ball and a piece of paper at the same time, it is pretty obvious that they would fall at different rates. The paper has a small mass compared to it's surface area, and the bowling ball has a larger mass compared to its surface area. It takes longer for the piece of paper to push away the air molecules, than the bowling ball.
So how come on the moon, a feather and a hammer fall at the same speed?
It has a lot to do with air resistance! Air resistance is the action of friction that slows something moving through air.
A vacuum surrounds the moon, and there is no matter in a vacuum. Therefore, on the moon there is no air resistance. So when Commander David Scott dropped the hammer and feather on the moon, the moon's gravity pulled both the hammer and the feather in at the same rate of acceleration. Because there is no air resistance to slow down the fall, the two objects fall at the same rate.
In the video posted below, Commander David Scott drops a hammer and a feather on the moon! Its an amazing video and thanks to physics, I understand how this is possible!