Class 6, 1/27/04, Summary
Reiterated items:
R1. Books reserved at Shields for this course. The link, titled
"Books reserved for Phy010B at Shields", is added to the course web page.
R2. The 2 and 5 on the scientific scale (HW SA2.3). (A student asked
the good question why the point 5 is not at the half-way point. To explain
that, unfortunately, it is off-limit from high-school math, although it is
not that complicated. That student deserves 0.5 bonus, please send me an e-mail.)
R3: Second law of thermodynamics (e.g., human getting old and die,
Murphy's law, etc.)
R4: The units for G, Newton's universal law of gravity, can be obtained
by balancing units of two sides of the equation of universal law of gravity.
R5: Chau derived again from Newton's second law combined with his
universal law of gravity that the accelertation from gravity is indeed universal,
in dependent of the mass of the accelerated object. That was first demonstrated
by Galelio empirically in his famouse experiment at the leaning tower of Pisa,
(way before Newton, who was born on the Chrismas day of 1642, the year Galileo
died). Chau showed an animation of Galileo's experiment.
New items (mainly about Chapter 5 of TB1)
N1: Since we live in three-dimensional space, the kinetic
energy has three parts (one for each direction), so does each of Newton's
laws. Commonly, the Cartesian coordinates are used.
N2: The force of universal law of gravity is in the
direction of the straight line drawn between the two object. Therefore,
we need to use the polar coordinates with the line between the two objects
being the radial direction. Thus, according to Newton's first law, the momenta
in the other two directions perpendicular to the radial direction are still
conserved.
N3. One of the two direction is the angular direction, which is
perpendicular to the radial direction. The conserved momentum in the angular
direction is called the angular momentum. The fact that a spinning dance
can speed up the spinning (the angular momentum) by pulling arms toward the
body is due to conservation of angular momentum. Kepler's second law is nothing
but the conservation of angular momentum. Chau showed an animation demonstrating
it, an interesting dancing of the planet (orbiting slower when far from the
heavier attractor and orbiting faster when closer).
N4. The other direction is the direction perpendicular to the plane
formed by radial and the angular direction. Since there is no motion in
this direction to begin with, there is always no motion in this direction.
Thus, the planetary orbit always lies on a plane.
N5. Newton's precise formula for Kepler's Third Law.
N6. Gravitational potential and escape velocity.
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Quiz 1 reminder and further guidelines:
* Please review carefully the Syllabus (on this web) for all
the detailed info and guidelines, if you have not yet done that.
* Quiz 1 covers these materials:
** Lectures 1 to 4,
** HW1 & HW2, and
** Reading assignments (both TB1 and TB2) of Week
1 and Week 2. (Please see Reading Assignment list on this web.)
* The quiz will have about ten problems. Most of them are short-answer
questions, some involving simple calculations like in HWs.
* Make sure that you know the important information clearly
, and understand the calculation procedures presented in lectures
and carried out in homework. As mentioned before, test material will be
mainly related to lecture and HW material. Material in reading assignment
not related to lecture or HW is less important, less than 30% of the quiz.
Preview of the class
* Reiterate some items of the previous class and the graded HW2.
* Wrap up Chapter 5 of TB1 and give some highlights of TB2 week 3 reading
assignment.
* Hand out graded HW2, with solutions written down for imperfect
answers. (This will be our form of giving solutions. Since we did not do
that for the graded HW1, we distribute the full solution of HW1 to all students,
to be handed out with the graded HW2.)
Please read the following before you fill out the sign-up
sheet.
Sign-up items (We will follow this routine notation from
now on. Please have the answers ready before class.)
* TB1: Finished reading Week 3 assignment of TB1 ?
Y, N.
* TB2 : Finished reading Week 3 assignment of TB2 ?
Y, N.
* Initial.