### Galileo's Experiment on Falling Bodies

• Our intuition, combined with supporting evidence from everyday experience/observations, suggests that heavier objects should (and do appear to) fall more rapidly than lighter ones.

• Indeed, based on everyday observation, Aristotle proposed that the rate of fall of an object was proportional to its weight. Many people believe intuitively that heavier objects fall faster.

• Galileo tested this hypothesis by droping objects of different weight and observing their fall (some say from the Leaning Tower of Pisa, although this story may be apocryphal)

• Nevertheless, he determined that bodies of different weight fall at the same rate.

• Indeed, Newton's Second Law (combined with the Law of Gravitation) shows that the rate of fall (that is, the object's acceleration) should be independent of its mass/weight.

• The force of gravity acting on an object (i.e. its weight) is proportional to its mass.

• The larger the mass the greater the force.

• An object accelerates, however, at a rate inversely proportional to its mass. So the increased force of gravity for a larger mass is exactly cancelled by the larger mass' resistance to being accelerated.

• All objects accelerate uniformly regardless of mass. Combining the two equations above

the mass of the object has cancelled out...

• Our intuitive perception that lighter objects fall more slowly than heavier ones is a manifestation of air resistance.

• In a vacuum all objects fall at the same rate.

Revised September 9, 2005