In the vacuum, does one kilo of feather fall more quickly or slowly than one kilo of lead? A video from the Moon gives us the answer.
Whether Galileo did make the experiment of the Pisa Tower or not is not important: he had a good understanding of the phenomenon of falling bodies and he proposed experimental checks of it using various techniques. But let us return to what he wrote about falling bodies.
"We propose to seek what would happen to falling bodies of very different weights in a medium completely devoid of resistance. If we find that the difference in speed depends on the capability to penetrate, and that for very unequal weights in an extemely empty medium although not in vacuum, the variation in speed is very small and virtually imperceptible, then we could admit with a very great probability, that speeds would be equal in vacuum".
Obviously, Galileo did not have the sufficient technical means to carry out his programme.
In homage to Galileo, the astronaut David Scott performed "Galileo's experiment" during the Apollo 15 mission, in July 1971. A feather and a hammer dropped from man height on the Moon reached the lunar ground at the same time. Though this experiment was not quantitative, it paved the way for similar experiments no longer on the Moon, but in drop towers.