90 likes | 282 Views
A History of Gravity: Aristotle through Cavendish. 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. The Pre-Modern “Universe”.
E N D
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
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
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
Isaac Newton: 1643-1727Puts 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! • Fg = GMm/R2 • Big idea, though he remained religious
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
Image References • Galileo portrait by Giusto Sustermans • Newton portrait by Godfrey Kneller • En.wikipedia.org