1. “It's a good thing we have gravity, or else when birds died they'd just stay right up there. Hunters would be all confused.” Stephen Wright

2. Universal Gravitation A History of Falling

3. Gravity It’s something we all know about from birth It is the first force we really experience and the one we think we best understand

4. How well do we understand it? The basic actions of gravity, that it attracts objects towards each other, is pretty basic In truth, it is the least understood of the fundamental forces

5. Misperceptions Heavy objects do not attract lighter objects, they both attract each other

6. Misperceptions Gravity is not the strongest force, it is in fact the weakest It is 10 36 times weaker than the electromagnetic force

7. Misperceptions Gravity in space is not zero All items in free space are being attracted by something There is no stationary frame of reference gravity is not noticed

8. The history In order to better understand gravity we must first know the history of the discovery The missteps of the past are always good to keep in mind

9. In the beginning… There are things about the natural world that are obvious and that all living things have evolved to deal with

10. The obvious We see in the range where the Sun is the brightest We live on water, the most abundant thing on Earth We are perfectly adapted, on the average, to move in Earth’s gravity

11. So what? Primitive man had many reasons to wonder at gravity and its affects There is evidence that early forms of hunting involved running prey off of cliffs and letting gravity do the rest

12. The celestial Mankind has always looked to the heavens and marveled at what they saw Even today, using advanced telescopes, we are amazed at the beauty of space

13. The celestial The repeated motions of the stars was the first thing to fascinate people The mechanisms behind this motion was not known to be gravity at the time

14. Mythology What early man could not explain got attributed to magic, spirits, and gods Prayers and sacrifices did little to change the motions of the heavens so this system was abandoned

15. What comes next When faith-based science fails a new system must be created

16. Age of Philosophy Philosophy came about because of the failures in random, unfounded beliefs Philosophy relies on pure thought, reason, and logic

17. The philosophers The first great philosopher was Socrates We have no direct evidence of his works, only what Plato, his student, wrote about him

18. Plato Plato established the idea that circles are the perfect shapes and that anything that is not a circle is somehow imperfect He taught Aristotle

19. Aristotle Not just a philosopher, but the first scientist Aristotle’s universe had the Earth at the center and all the planets and stars set into large crystal spheres

20. Crystal Spheres It was thought by ancient philosophers that all motion was due to contact of some sort The crystal spheres contacted the planets and moved them What moved the the spheres is anyone’s guess…

21. Aristotle’s Universe It agrees with basic observations Essentially correct, but horribly wrong

22. Aristarchus The first person to predict that the Sun is the center of the solar system Had some logical flaws Ignored and rejected because of Archimedes

23. Aristotle on gravity The motion of Earth-bound objects was described in Physics Objects fell in straight lines, the heavier objects falling faster than lighter ones

24. The disconnect The Greeks never saw a connection between the motion of falling bodies and the motion of the planets Silly Greeks

25. Physics Aristotle’s Physics was the definitive work on the subject until the Renaissance period All other scholarly work in physics consisted of commentaries on Physics

26. Ptolemy (the P is silent) It was obvious to many observers that the simple circular cycles were wrong Ptolemy invented the idea of epicycles, in which planets revolved in small circles which themselves revolved on larger circles