What is Gravity? This lecture reviews the law of falling bodies first

described by Galileo, and then Newton's explanation in terms of his Law

of Universal Gravitation. Gravity is a mutually attractive force that

acts between any two massive bodies. Its strength is proportional to

the product of the two masses, and inversely proportional to the square

of the distance between their centers. We then compare the fall of an

apple on the Earth to the orbit of the Moon, and show that the Moon is

held in its orbit by the same gravity that works on the surface of the

Earth. In effect, the Moon is perpetually "falling" around the Earth.

Recorded 2006 Oct 16 in 100 Stillman Hall on the Columbus campus of The

Ohio State University.