Galileo was the first to assert that all bodies at rest fall at the same velocity, regardless of their material, weight, and volume. Experiments showed, however, that heavier bodies reached the ground far sooner than lighter ones.

Galileo argued that such an anomaly was due to the resistance of air and that, absent such a force, all falls would prove to be of equal duration. In the late seventeenth century, thanks to the development of instruments that made it easy to create vacuums, an ingenious apparatus was built that finally allowed an experimental demonstration that Galileo was absolutely right. A vacuum was created in a glass tube by means of a pump. A feather and a gold coin (a guinea) placed inside the tube were dropped at the same time. The two bodies, despite their very different weights, reached the base of the tube together.