1. Force – An interaction between two objects resulting in a push or a pull.
Aristotle (384 – 322 B.C.)

2. Aristotelian Physics
Earthly (Sublunary) Region – The abode of change and corruption, where things came into being, grew, matured, decayed, and died
Cosmos
Heavens – The region of perfection, where there was no change.
Earth – The heaviest of the four elements whose natural place was the center of the cosmos.
Sublunary Region
Water
Air
Fire
Filled with aether (quintessence), whose motion was in perfect circles. Each planet had its own spherical shell of aether that moved constantly at its own speed with no space between them.
Heavens

3. Aristotelian Physics
Natural Motion – Motion resulting from an object trying to reach its natural place. Either straight up or straight down.
Motion
Violent Motion – Motion imposed on an object by an outside force – Motion only lasts as long as the force.

4. Ptolemy (2nd Century AD)

5. Ptolemaic (Geocentric) Solar System

6. Ptolemaic Solar system had 40 different epicycles and deferents.
Explanation of observed retrograde motion of certain planets in the Ptolemaic system
Demo
Ptolemaic Solar system had 40 different epicycles and deferents.

7. Nicolaus Copernicus (1473-1543)

8. Copernican (Heliocentric) Solar System
De Revolutionibus Orbium Coelestium ("On the Revolutions of the Celestial Orbs"), which was published in Nuremberg in 1543, the year of his death.

9. Problems with the Copernican (Heliocentric) Solar System
The “impossibility” of a moving Earth.
Religious implications.
Lack of stellar parallax.

10. Parallax Problem

11. Since the Earth is so far away from the stars, the effect of parallax is minimized.

12. Galileo Galilei ( )
Inertia – The tendency of an object to continue in its same state of motion.

13. Sir Isaac Newton (December 25th, 1642-1727)
Newton’s First Law of Motion – An object will continue in its same state of motion unless acted upon by a net force.
Net Force - vector sum of the forces