According to legend, in 1590, Galileo made an experiment of "two iron balls landing at the same time" on the leaning tower of Pisa, and came to the conclusion that two iron balls with different weights fell at the same time, thus overthrowing Aristotle's theory that "the falling speed of an object is proportional to its weight" and correcting this erroneous conclusion that lasted for more than 1900 years.
Extended data
The speed of free fall is extremely fast. In order to reflect the different falling distances caused by the different falling speeds of heavy objects and light objects, a considerable height is needed to form this difference. This is why the free fall experiment should be carried out on the highest local building of more than 50 meters.
According to the records of Galileo's student V. Vivienne in his later years, a falling experiment was carried out on the leaning tower of Pisa, but it was not recorded in Galileo's works, so it is generally considered unreliable.
Galileo made a detailed study on the basic concepts of motion, including center of gravity, speed and acceleration, and gave a strict mathematical expression. Especially the concept of acceleration is a milestone in the history of mechanics. With the concept of acceleration, the dynamic part of mechanics can have scientific basis, while before Galileo, only the static part was described quantitatively.
References:
Baidu encyclopedia-law of free fall