March 1, 2000

Pressure Vs. Gravity round II


 
 [Socrates continuing the argument that medicine- a science - and the art of speaking are similar]"...In both cases we need to determine the nature of something - of the body in medicine, of the soul in rhetoric. Otherwise, all we'll have will be an empirical and artless practice." 
Plato, Phaedrus, 4th century B.C.
  Start reading Chapters 27, 28. Look up announcements for new extra credit possibilities.. HW#4 solutions are now available.
Pressure Push vs. Gravity Pull- A Quantitative Description:

Gravity prop. to total masses of a large "lump" or clump of material, and the mass being pulled.

Question 1:
The gravitational pull by the small star on a 1 cubic meter of material is ______ that of the pull by the large star
1. ½
2. twice
3. four times
4. ¼
5. 3.1412 times
(Used for other questions).
Answer: 1/2

Gravitational pull is inversely proportional to the distance between the two masses pulling on each other. 

Question 2: The gravitational pull by the left star on a 1 cubic meter of material is ______ that of the pull by the right star. Answer: 1/4

What holds the star from collapsing on and on? Pressure does. The particles that pull on each other also move. Train station analogy. 
Bumping = pressure. 

When there are more particles (people in the station) - more bumping.

So the higher the density - the higher the pressure.

Question 3: The pressure push by the star on a 1 cubic meter of density 1kg/Meter^3 of material is ______ that of the push by the star on a 2 kg/Meter^3. Answer: 1/2.

Pressure push also depends on how fast the "particles" in the station are moving.

Faster particles = higher temp.

Higher temp = higher push (pressure)

Question 4: The pressure push by the star of temperature 10,000K on a 1 cubic meter of material with temperature 10,000 K  is ______ that of the push by a star with temperature 2500 K. Answer: four times.

Summary: 
If Gravitation pull > pressure push the gas cloud / star shrinks.

If push > pull the star grows in size.

If push = pull the star is usually stationary. 
 

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