Four Forces of Nature - part II.

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&#2  changed to intensity.

Regarding subject matter: 

Short film on solar evolution.

ON BB:  LEFT: CIRCLE OF DANCERS. RIGHT: HERSZPRUNG RUSSEL DIAGRAM
Relate everything to E=mc^2 and energy conservation.

The plasma dance:

1. Gravity: Like a dance party. The force that brings everybody together is gravity. (At long range, everybody & everything is attractive!)
Electrons & Nuclei come mostly in "pairs". The electrons "Waltz" around the the nuclei (Fat guy & thin lady or opposite.)

It gets hotter. Why? Speeding up towards the party (free fall demo). Colliding with other pairs.

DEMO with gravity & increasing density.

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. 

Question: What will be the result of such excitement/excitations?

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.)

Question: When stars are being born they are actually bright and blue for about ONLY one million years. What happens then? Use the party analogy, or the fuel/consumption analogy.

How about closer to the center of things in the party? Things get really wild there!

Show transperancy:

In the center of the "party", (I should probably stop with the analogy here, or trouble...)
+ &+ move so fast that they may actually stick together!

Demo: carts.

3. Strong force:
Nuclei overcome their attraction and stick together with Velcro-like force. Very strong, very short range.

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... 
In the process an anti-particle is created, and an elusive particle called neutrino, and the new pair is SO excited that they emit gamma rays, and lose lots of mass!

Question: If Gamma rays are emitted in the center of the sun, how come there is so little gamma rays coming out? What happens to the energy of ONE GAMMA RAY PHOTON as it is traveling outwards towards the surface of the sun?
 

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.