1. A History of Gravity: Aristotle through Cavendish

2. Ancient and Pre-Modern Theories Aristotle’s theory of four elements – Earth moves to earth, heavier objects fall faster Astronomy and Astrology exist But Heavens are considered to be a separate realm from Earth

3. The Pre-Modern “Universe” Objects in Heavens (stars) are fixed to crystalline “spheres,” nested around Earth Ptolemy’s Geocentric Theory (90 – 168 ACE) Heavenly objects presumed to follow principles distinct from objects on earth

4. Galileo and the Scientific Revolution: 1564-1642 Pioneered testing theory with experiments Ramp experiments: showed bodies of any mass have the same acceleration Found period of pendulum independent of mass

5. Isaac Newton: 1643-1727 Puts it all together Worked from astronomers’ data Asked what made moon orbit the earth Apple on head story: The same force acts on objects and planets! F g = GMm/R 2 Big idea, though he remained religious

6. Weighing the Earth: Henry Cavendish (1731-1810) Set up sensitive apparatus designed by a friend Wanted to “weigh the earth” Measured Mass, Force, Distance Could figure out G Got within 1% of modern accepted value Force was 1x10 -7 N

7. Image References Galileo portrait by Giusto Sustermans Newton portrait by Godfrey Kneller En.wikipedia.org