Experiments have been done in a lot of interesting places, but perhaps none could be more interesting than on the surface of the moon. In the 16th century, Italian scientist Galileo Galilei supposedly came up with the hypothesis that all objects accelerate at the same rate, regardless of their mass. This was in contrast to Aristotle's theory of gravity in use at the time, and which stated that all objects fall at a speed proportional to their mass. To test his theory, Galileo supposedly dropped spheres of different masses off the leaning tower of Pisa, although whether this experiment ever actually took place is contested.
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| NASA/James B. Irwin / Public domain |
While objects do accelerate at the same rate, air resistance limits the maximum velocities of objects and this is termed terminal velocity. Under normal circumstances this means that light objects with a large surface area such as a feather would stop accelerating rather quickly and have a low terminal velocity, allowing heavier items with a higher terminal velocity to pass them. On the moon however, the air is much thinner. This means that the moon is a much more ideal place to demonstrate this experiment as you do not need to worry about air resistance slowing down the feather. Due to this, in theory, on the moon both the hammer and the feather should accelerate at the same rate and hit the ground at the same time.
For the Apollo 15 recreation of the test they decided to use a falcon feather to match the Falcon callsign of the Apollo 15 lunar module as well as a 1.3 kg aluminium and steel geological hammer. In the clip, after a brief introduction, astronaut David Scott can be seen releasing the hammer and the feather at the same time, and they both fall at exactly the same rate hitting the ground at the same time.
