A History of Gravity: Aristotle through Cavendish - PowerPoint PPT Presentation

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A History of Gravity: Aristotle through Cavendish
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A History of Gravity: Aristotle through Cavendish

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  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: 1643-1727Puts 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

  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