Tower of Pisa

La Torre di Pisa (Opera Primaziale Pisana)

The gravity experiment: unlike what we find written in many manuals, Galileo never carried out the gravity experiment from the famous Tower, but he studied Aristotelian notions and questioned them in a theoretical way, or with limited experimental evidence. Aristotle claimed that bodies fall in direct proportion to their own weight, so the heavier a body, the faster it falls. Galileo, however, only remained faithful to the notion, also Aristotelian, according to which bodies fall with a uniform speed depending on their density. He knew perfectly well the resistance that air exerts on the volume of a body, therefore he deduced that: …and for this [the experiment can be carried out] we need a space entirely devoid of air and any other body [...] since we lack such space, we will observe what happens in the subtlest and least resistant mediums [...] it seems to me that we can very probably believe that in vacuum their speeds would be quite equal. With this statement he makes us understand that, in the absence of friction, in a condition that we today define as ideal, the fall would be the same. Of course, the Tower would never have been that ideal place, so it is reasonable to say that this experiment never took place.