Catalog of Sites and Images

Lecture: Gravity

Don't Panic

Hopetoun Falls, Beech Forest, near Otway National Park, Victoria, Australia.

Credit: Wikipedia contributor David Iliff. According to Wikipedia permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version.

Download site: Wikipedia: Image:Hopetoun falls.jpg.

Sections

1. Alphabetic Listing
2. Lecture Listing

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Alphabetic Listing

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1. Images.

2. Cambridge University Images.

3. Centrifugal force Images.

4. Earth's rotation Images and animations. See the Earth turn even faster than the astronauts. The Earth's mean angular velocity is 7.2921150*10**(-5) radians per second. The Earth's rotational kinetic energy is of order 2.5*10**29 J (Wikipedia: Rotational energy).

5. Escape velocity Images.

6. Galaxies Images. See the See galaxy rotation curve.

7. Gauss's law for gravity No images.

8. Gravitation Images.

9. Gravitational potential energy Images.

10. Greek alphabet Images.

11. Gravitational two-body problem Images and animations.

12. Isaac Newton (1643--1727) Images.

13. Johannes Kepler (1571--1630) Images.

14. Kepler's laws of planetary motion Images.

15. Lunar eclipses Images and animations. The 2008feb20 eclipse

16. Newton's apple Images.

    Not the tree, but maybe is a descendant).

    The falling apple story is probably true since it came straight from the horse's mouth so to speak.
    "when formerly, the notion of gravitation came into his mind. It was occasioned by the fall of an apple, as he sat in contemplative mood. Why should that apple always descend perpendicularly to the ground, thought he to himself. Why should it not go sideways or upwards, but constantly to the earth's centre."---William Stukely (1687--1765).

17. Newton's laws of motion Images.

18. Newtonian physics Images, but nothing great.

19. Orbit Images and animations.

20. Orbit of the Moon Images and animations.

21. Orbital speed No images. Tables.

22. Principia Images. He wrote it in Latin under the impression that that would make it more accessible.

23. Universal law of gravity Images.

24. Westminster Abbey Images.

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Lecture Listing

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1. Isaac Newton (1643--1727) Images.
   A man from the dawn the of the Age of Reason

   The Godfrey Kneller's 1689 portrait: the Newton of the Principia, the man in his prime.

   The hair's phony I think.

2. Cambridge University Images.
   Newton was a student and then a professor at Trinity College, Cambridge. See the Great Court of Trinity College which dates back to Newton's day.

   When an undergraduate he had to retire to his home in Lincolnshire to wait out the plague of 1665--1666 and that is where some of his earlier great discoveries in gravitation were made.

   See the Bill of Morality 1665.

3. George Washington had his cherry tree, (see cherry tree in Lebanon) and Newton had his apple tree (of which this apple tree) maybe is a descendant).
   The falling apple story is probably true since it came straight from the horse's mouth so to speak.
   "when formerly, the notion of gravitation came into his mind. It was occasioned by the fall of an apple, as he sat in contemplative mood. Why should that apple always descend perpendicularly to the ground, thought he to himself. Why should it not go sideways or upwards, but constantly to the earth's centre."---William Stukely (1687--1765).

4. Orbit Images.
   Now Newton didn't discover gravity.

   What he discovered was that the force that made apples fall, pulled the planets into orbits.

5. Newton's reflector. It's a facsimile.
   As well as the theoretical natural philosopher---Newton's would not have heard of the word physicist---Newton was also an experimenter and inventor.

   He wasn't the first person to think of a reflecting telescope, but he was the first it seems to build a working model.

   Scroll down on reflecting telescope to see the Newtonian reflector schematic diagram.

6. Orbit Images and animations.
   Newtonian physics allowed Newton and us to understand Orbits.

   To illustrate how orbits arise Newton can up with Newton's Mountain as we now call it. Apparently, this doesn't appear in the Principia, in a later popularization The System of the World---but there is some unclarity in the online sources.

   The ideal case is two isolated bodies.

   They orbit about their mutual center of mass. See orbit animation.

   If one bodies is much more massive than the other, then it is effectively the center of mass: this is approximately true for the Sun-Earth system and more approximately true for the Earth-Moon system.

   See the Orbit of the Moon and the Earth-Moon orbit animation

7. inertial frames Images, but nothing great.
   Newtonian physics must be referenced to inertial frames.

   Inertial frames are fundamentally unaccelerated frames and somehow are determined by the nature of space or in modern physics spacetime.

   Newtonian physics is still valid in non-inertial frames, but it's not referened to them.

   In non-inertial frames, one can have accelerations without a force---without real forces---there are these fictitious or inertial forces which are just the effects of being in a non-inertial frame.

   For example, the inertial forces, centrifugal force and the Coriolis force both of which appear in rotating frames.

   The centrifugal force is just the ``force'' that tries to throw you out of the rotating frame and Coriolis force is an effect of moving in the rotating frame.

   See the rotating parabolic disk animation which unfortunately is complicated by the parabolic shape of the disk for the bouncing particle---so four effects are going on at the same time centrifugal force, Coriolis force, gravitational force accelerating the particle, and collisions.

   On the left, one sees the system from a rest frame.

   On the right, one sees the system from the rotating frame.

   The particle actually collides with the same point on the surrounding wall all the time actually.