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Announcements

Announcements. Take the test any time today, tomorrow, or Friday before class. Bring photo ID. Allow one hour. After you’ve taken the test, don’t discuss it with classmates until class on Friday. Copernicanism may be fine for astronomy, but.

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Announcements

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  1. Announcements • Take the test any time today, tomorrow, or Friday before class. Bring photo ID. Allow one hour. • After you’ve taken the test, don’t discuss it with classmates until class on Friday.

  2. Copernicanism may be fine for astronomy, but . . . • If the earth is moving, why don’t we feel the motion? • Why aren’t we thrown off a spinning, orbiting earth? • What possible mechanism could cause planets to move in elliptical orbits? • If gravity isn’t a tendency of stuff to fall toward the center of the universe, then what is it?

  3. Newtonian Mechanics 20 September 2006

  4. Course Outline • Naked-eye astronomy • Crash course in physics • Our solar system • The stars • Structure and history of the universe

  5. Course Outline • Naked-eye astronomy • Crash course in physics • Our solar system • The stars • Structure and history of the universe You are here

  6. Today: • The law of inertia • How the motion of an object changes due to interactions with nearby objects

  7. Isaac NewtonEnglish scientist and mathematician, 1642 - 1727

  8. Why do things move? Aristotle: To seek their natural place in the universe. Newton: No reason. Motion just happens. More precisely: Isolated objects will coast along in a straight line, at constant speed, forever. (Speed = zero is just one example.) “Law of Inertia” or “Newton’s First Law”

  9. Consequence: Motion is relative.

  10. Consequence: Motion is relative. There’s no way to tell who’s really moving!

  11. Strobe Diagrams • Isolated object, moving to the right: 1 2 3 4 5 6 • Kick from the left at point 3: kick 1 2 3 4 5 6

  12. kick • Kick from the right at point 3: 1 2 3 4 5 6 • Kick from above at point 3: kick 1 2 3 4 5 6

  13. Continual kicks toward a fixed point (Principia, page 40)

  14. Newton’s Second Law Force applied Change in motion = Mass of object So the same force applied to a ping-pong ball produces a bigger change in motion than when applied to a bowling ball.

  15. In Newton’s own words (translated)

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