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Four Forces of Nature - part II.
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Read Chapter 26.1-6. Read sections 2-5 chapter 4, chpater 5 as preperation for next week.. HW#3 is now available. Watch the third CD movie (guided tour) on lives of stars. |
Announcements:
Lab #4 write ups: Distribute Links link linked... Regarding observation labs: If you did them: You can hand them in this week on my door. If not: 1/3 letter grade, so sign up & come as soon as possible! There were 12, good nights so far, 9 undersubscribed. If you haven't gotten into them, you have to have an excuse for each & everyone! Help session with problem sets #3 & #4: Tuesday evening? 7:30? Corrections to HW#3 : Flux in problems #1 changed to intensity. Regarding subject matter: Short film on solar evolution. ON BB: LEFT: CIRCLE OF DANCERS. RIGHT: HERSZPRUNG RUSSEL DIAGRAM
The plasma dance: 1. Gravity: Like a dance party. The force that
brings everybody together is gravity. (At long range, everybody & everything
is attractive!)
It gets hotter. Why? Speeding up towards the party (free fall demo). Colliding with other pairs.
How many pairs? Its quite a party! trillions of trillions of trillions of trillions come (10^57 atoms are the pairs for the sun). Now square dancing begins! That's what happens in the chromosphere of the sun.
Everytime a pair is excited - some emission lines (wahoo!). Its the first demo of E=mc^2. Energy of motion is converted into excitations. When light is emitted from those atoms they are actually slightly less massive. Eventually, pairs are broken. Ionization (lab#2!). (Switch your partner!) This is plasma, and plasma is when wild things happen! 2. Its the Electromagnetic force most active now. - attracts +. + -. You find your same especially repulsive... - repel -. Still a "mild" plasma (density of earth's atmosphere, temp. of 4500 K.) Its called the chromosphere. The "cold" gas responsible for absorption lines in the sun's spectrum, and other stars. Its getting to be really dense dance now. Can't quite tell who's with whom. That's when the emission is all over the place. No distinction. (Rainbow spectrum. Blackbody spectrum.)
How about closer to the center of things in the party? Things get really wild there!
In the center of the "party", (I should probably stop with the analogy
here, or trouble...)
3. Strong force:
Very unstable situation! Wave properties of particles: only survives for a short while., then breaks. All energy to stick-em is lost... Unless.... 4. Weak force: One of the two + nuclei, (protons) is changing
its character by losing its repulsive properties...
Eventually 2 such pairs are joined to make a quadrople, called Helium nucleus with less mass. Question: Given the mass difference from the periodic table, how old is the sun? Let's summarize: The four forces of nature are responsible for turning mass into energy. Gravity does it indirectly, through heating gas up and letting it cool off by emission. E&M forces make a plasma what it is. The strong force supplies the glue that enables turning m into massive quantities of E, but if not for the weak force it wouldn't work in the sun.
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