1. Foundations-Copernican Revolution Lecture 3: Newton: Gravity and the Laws of Motion

2. Ancient Observatories Ancient Peoples around the world made places to mark dates from the celestial calendar and/or observe the sky  Chaco Canyon, New Mexicohttp://www.exploratorium.edu/ancientobs/http://www.exploratorium.edu/ancientobs/  Chichen Itza http://www.exploratorium.edu/ancientobs/ http://www.exploratorium.edu/ancientobs/  Angor Wat, Cambodia  Medicine Wheel, Saskatchewan, Canada  Stonehenge, England  Abu Simbel, Egypt

3. Science vs. Pseudo-science  What makes science different?  What do we know?  How do we know it?  Why do we believe it?  Is what we know supported by the evidence?  Kuhn Paradigm  Thomas Kuhn: Structure of Scientific Revolution  Navigating the web of a 1000 lies

4. End of the world in 2012? December 21, 2012 See National Geographic and NASA websites on thisNational Geographic NASA  Mayan Calendar – long count calendar enters a new cycle Each cycle is 5,125.37 years–  The sun will cross in front of the center of the Milky Way But this has happened many times before No significant increase in gravitational interaction  Sun will be in solar maximum – more solar flares and storms This has happened may times before  A tenth planet known to the ancients that would hit us by end of the year would be visible to astronomers for past decade Why the hype?

5. a) planets move on epicycles. b) planets orbit the Sun in the same direction. c) Earth moves faster in its orbit. d) they are closer than Uranus. e) they rotate quickly on their axes. Mars, Jupiter, and Saturn show retrograde motion because Question 1

6. a) planets move on epicycles. b) planets orbit the Sun in the same direction. c) Earth moves faster in its orbit. d) they are closer than Uranus. e) they rotate quickly on their axes. Mars, Jupiter, and Saturn show retrograde motion because Question 1 As Earth overtakes and “ passes ” the outer planets, they seem to slow down and then reverse direction.

7. a) why planets moved in the sky. b) why Earth was at the center. c) why retrograde motion occurred. d) why Earth wobbled on its axis. e) why inner planets were always seen near the Sun. Epicycles were used in Ptolemy ’ s model to explain Question 2

8. a) why planets moved in the sky. b) why Earth was at the center. c) why retrograde motion occurred. d) why Earth wobbled on its axis. e) why inner planets were always seen near the Sun.. Epicycles were used in Ptolemy ’ s model to explain Question 2 Planets were assumed to move uniformly on an epicycle, as it moved uniformly around Earth.

9. a) craters on the Moon b) sunspots c) lunar maria d) satellites of Jupiter e) stars of the Milky Way Which of Galileo ’ s initial observations was most challenging to established geocentric beliefs? Question 3

10. a) craters on the Moon b) sunspots c) lunar maria d) satellites of Jupiter e) stars of the Milky Way Which of Galileo ’ s initial observations was most challenging to established geocentric beliefs? Question 3 Seeing four moons clearly move around Jupiter disproved that everything orbited Earth and showed Earth could orbit the Sun and not lose its moon, too.

11. Galileo (1564-1642) Built his own telescope. Discovered four moons orbiting Jupiter => Earth is not center of all things! Discovered sunspots. Deduced Sun rotated on its axis. Discovered phases of Venus, inconsistent with geocentric model.

12. Phases of Venus The phases of Venus are impossible to explain in the Earth-centered model of the solar system.

13. Timelines of the Big Names Copernicus Galileo Brahe Kepler Newton 1473-1543 1546-1601 1473-1543 1564-1642 1571-1630 1642-1727

14. Kepler (1571-1630) Used Tycho Brahe's precise data on apparent planet motions and relative distances. Deduced three laws of planetary motion.

15. Question 4 Earth is closer to the Sun in January. From this fact, Kepler ’ s 2 nd law tells us a)Earth orbits slower in January. b)Earth orbits faster in January. c)Earth ’ s orbital speed doesn ’ t change.

16. Earth is closer to the Sun in January. From this fact, Kepler ’ s 2 nd law tells us a)Earth orbits slower in January. b)Earth orbits faster in January. c)Earth ’ s orbital speed doesn ’ t change. Kepler ’ s 2 nd law means that a planet moves faster when closer to its star. Faster Slower Question 4

17. Kepler's First Law The orbits of the planets are elliptical (not circular) with the Sun at one focus of the ellipse. Ellipses eccentricity = (flatness of ellipse) distance between foci major axis length

18. Kepler's Second Law A line connecting the Sun and a planet sweeps out equal areas in equal times. Translation: planets move faster when closer to the Sun. slower faster

19. Kepler's Third Law The square of a planet's orbital period is proportional to the cube of its semi-major axis. P 2 is proportional to a 3 or P 2  a 3 (for circular orbits, a=b=radius). Translation: the larger a planet's orbit, the longer the period. a b

20. 3. Square of period of planet ’ s orbital motion is proportional to cube of semimajor axis. Kepler ’ s laws: 1.3 The Laws of Planetary Motion

21. At this time, actual distances of planets from Sun were unknown, but were later measured. One technique is "parallax" "Earth-baseline parallax" uses telescopes on either side of Earth to measure planet distances.

22. Newton (1642-1727) Kepler's laws were basically playing with mathematical shapes and equations and seeing what worked. Newton's work based on experiments of how objects interact. His three laws of motion and law of gravity described how all objects interact with each other.

23. Newton's First Law of Motion Last time – Demo of objects at rest Demo – nature of how objects move  Hover disk

24. Newton ’ s laws of motion explain how objects interact with the world and with each other. Newton ’ s first law: An object at rest will remain at rest, and an object will move in a straight line at constant speed if and only if the sum of forces that act on it are balanced. 1.4 Newton ’ s Laws

25. Newton's Second Law of Motion When a force, F, acts on an object with a mass, m, it produces an acceleration, a, equal to the force divided by the mass. a = F net m or F net = ma acceleration is a change in velocity or a change in direction of velocity.

26. Newton's Second Law of Motion Demo - Force and Acceleration Fan Carts