Physics 101- Introduction to Mechanics
February 11- Newton's Laws






  Planetary Motion
  • The motion of the planets was the main driving force in early physics- they knew nothing of atoms so they didnít worry about them.
  • Understanding the motion of the stars was important- gave us a glimpse into the heavens.
  • Earlier models of the universe relied on philosophy or religion and not careful observations.
  • Galileo was one of the first to actually try and make quantitative observations of motion.
  • Kepler wasnít trying to understand why the planets moved the way they did; he simply wanted to find the pattern. 
  • Kepler said that the planets moved in ellipses- but didnít say why this was the case. 
  • Newton actually formulates the laws of physics and explains why the planets move the way they do.  And, to do this he invented calculus.
  • Newton's theories are valid for both planets and balls flying through the air.


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Jeff Phillips
Loyola Marymount University
Spring 2002