Galileo held a feather and a stone in either hand and 

released them simultaneously. Because the feather's structure slowed its descent in parachute fashion, the stone reached the Earth first. Had both been released above the Moon's surface, where no air exists, each would have struck the lunar surface simultaneously. It was not until Astronauts David Scott and Jim Irwin conducted Galileo's experiment on the Moon during their Apollo 15 mission that the experiment could be duplicated in the lunar environment.

    A heavy object (a 1.32-kg aluminum geological hammer) and a 

light object (a 0.03-kg falcon feather) were released at the same time from approximately the same height (approximately 1.6 m) and were allowed to fall to the surface and hit at exactly the same time.

Click here to watch the video of this experiment. http://nssdc.gsfc.nasa.gov/planetary/image/featherdrop_sound.mov