One of the most common examples of uniformly accelerated motion is that of an object allowed
to fall freely near the Earth’s surface. It was widely believed until the time of Galileo that heavier
objects fall faster than lighter objects and that the speed of fall is proportional to how heavy the
object is.
Aristotle believed heavier objects fall to the ground faster than lighter objects. As legend has it,
Galileo dropped two objects from the Leaning Tower of Pisa to disprove Aristotle theory. These
objects were the same size, but different weights. They fell to the ground at the same speed. This
disproved Aristotle’s theory and led Galileo to discover the Law of Falling Bodies.
To support his claim that falling objects increase in speed as they fall, Galileo made use of a
clever argument: a heavy stone dropped from a height of 2 m will drive a stake into the ground
much further than will the same stone dropped from a height of only 0.2m. Clearly, the stone
must be moving faster in the former case.
As we saw, Galileo also claimed that all objects, light or heavy, fall with the same acceleration,
at least in the absence of air. If you hold a piece of paper horizontally in one hand and a heavier
object in the other, and release them at the same time, the heavier object will reach the ground
first. But if you repeat the experiment, this time crumpling the paper into a small wad, you will
find that the two objects reach the floor at nearly the same time.