Class 7, 1/27/05, Highlights

* Calculated the escape velocity from the surface of the Earth
    ** Showed how to calculate the square of it;
    ** Showed how to take square root without a calculator (See the web link about it for the class).
        *** Note added after class: Remember first to express the quantity in 10^(even number). For example, to take square root of 2.3x10^5, first convert it to 23x10^4. The example we worked out in class happen to have even powers of 10, so Chau forgot to mention this important point.

* Added the definition of angular velocity to HW4, SA4.1
    ** angular velocity, denoted by omega, = angle (in radian) turned per unit time; so its MKS unit is 1/s.
   ** angular momentum L= Mr^2 omega = Mrv, as TB1 gives it on p. 137.

* Go over Kepler's three laws, P.72, 73, and its more better understanding from Newton's universal law of gravity, p.139 - 140.
    ** Kepler's first law should include circles
    ** Kepler's second law is a result of the conservation of angular momentum. Chau showed the animation.
    ** Kepler's third law is more precisely given by the equation given on p.140, and HW4, multiple choice (9).
    ** Chau also showed the animation about ellipse, and definition of semimajor, semiminor, and eccentricity. (See the web link for the class.)

* Each planet moving around the Sun has its unique angular momentum, and during its motion the angular momentum states the same. So it is like doing a dance  (like the spinning skater), during which  r and omega can vary, but (r^2) x (omega) state the same.

* So, we finished discussing the reading material of the week, as listed below. Please try to finish reading them before the class.   
p.129-151, Chpt 5 of  TB1: The Universal Laws of Motion ;
p.53-p.84, Chpt 3 of TB2: Of Warps and Ripples.

* We finished discussing HW4.

* Our viewing of  the scientific biography video about Einstein and his theory of general relativity was not successful, due to some technical problems. (The irony was that as soon as the students left, Chau played it again and it worked!! Such is the frustration of using multimedia.) We will view it on some future occasion.