Engineering Expert Witness Blog

      Last time we discussed how Galileo proved Aristotle’s theory regarding the physics of falling objects to be wrong, although his experiment, which took place on the infamous Leaning Tower of Pisa, did not actually prove his own theory to be correct.   So why didn’t Galileo go the extra mile and prove his theory?  Because he couldn’t.

      Galileo, of course, resided on Earth, which was also the arena in which his experiment took place.   As such, both he and his experiment were subject to the physical constraints presented by the Earth lab, the single most influential factor being the impact of the planet’s atmosphere upon his falling objects.

      Put another way, contrary to popular belief at the time, air is not an empty, innocuous space devoid of physical properties.   It’s actually a gaseous soup of molecules.  Nitrogen, oxygen, carbon, hydrogen, and other elements are in the mix, and they all have mass, that is, weight within a gravitational field.   As Galileo’s balls fell, they continuously bumped against these molecules, which slowed their descent.   This air friction will be discussed later in our blog series.

      But in order to prove Galileo’s theory correct beyond a shadow of a doubt, the testing arena would need to be one free from the interference of atmosphere.   The Moon fits this criterion and provided the perfect environment to prove, once and for all, that Galileo’s theory was correct.   So when astronauts Scott and Irwin simultaneously dropped a hammer and feather to the Moon’s surface, both objects hit at precisely the same moment.   Watch this captured live footage of the event to see for yourself:

      One thing you may have noticed while watching the astronauts’ experiment is that the hammer fell more slowly than it would have on Earth.   This has nothing to do with the absence of atmosphere on the Moon, but it has everything to do with gravity.   We’ll discuss gravity’s influence in detail next time.

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