Class 12 and Discussion 6,  2/15/05

Class Hightlights
* Hydrogen is made of one proton and one electron
* Electric charges are quantized, i.e., discrete numbers in an universal unit, denoted by e (like in eV).
* In the unit of e, lectron has charge -1, proton has charge +1.
* Anti-matter was predicted by the Dirac equation.
* Each particle has its anti-particle, which has the same rest mass but opposite charge. So anti-electron, also called positron, has +1 charge. Anti-proton has -1 charge.
* Matter and anti-matter anahilate to produce photons, the radiation energy. For example, electron and antielectron annihilate to make two photons.
* From energy conservation, the photon frequence can be claculated.
* Showed the diagram of all know elementary constituent of matters: three families of quarks, three families of leptons, and the mediating particles of four forces.
* The mediating particles of three forces are experimentally observed:
    ** photon for electromagnetic force
    ** gluon for strong force
    **  W, Z bosons for weak forces
* The mediating particle for gravity, called graviton,  is not yet observed.
* The kinetic energy is composed of three parts, one corresponding to each dimension of the space.
*  The kinetic energy of a planet moving around the Sun is composed of the radial part and the angular part.

Discussion Highlights
* Discussed HW SA7.3.
* Discussed the concept of centrifugal potential energy. (It is actually the kinetic energy associated with the angular motion. When expressed in terms of angular momentum, it gains a 1/r^2 behavior, looking like a potential energy! So, be careful not to be confused with gravitational potential.)
* Reviewed angular velocity
* Reviewed gravitational potential energy
* Reviewed HW SA5.3 (typoed as SA6.1)


Preview
We will discuss the following materials. Please have a first full reading of them before the Tuesday class. As indicated in class, and now in Guidelines for Study and for Exam Preparation, the important Math Insights in TB1 are those covered in lectures and HW's. (Dr. Chau always tries to simplify them and make them more precise and up-to-date.)  Therefore, you can skip them in your first reading before the lecture.

Week-7 (2/13-2/19)
  · TB1, p.476-493, S4 , "Building Blocks of the Universe";
  · TB2,  p.117-165,  Chpt 5, "The Need for a New Theory: General Relativity vs. Quantum Mechanics," and Chpt 6,  "Nothing but Music : The Essentials of Superstring Theory."