Why Gravity Matters

1
Why Gravity Matters

2
A Question of Formation

• Big round hot things (like stars and planets)
  have real trouble cooling off. But why should
  there be any in the first place?
• In short, what made the stars and planets?
• And why are they inevitably round?

3
The Final Crucial Ingredient Gravity

• We already saw its importance for the giant ant,
  and for Robert Wadlow. But for them it is an
  external influence. (They are pulled down
  against the Earths surface.)
• What about self-gravity?

4
Visit the Barber
5
Lessons in Self-Gravity

• Why is the Earth spherical?
• Why are ants and people not?
• What is the critical size or mass that matters?

6
A Warning

• Note the meaning of the words mass and massive
  -- not the same as big

7
Meet an Asteroid
8
Meet a Planet
9
Sizes of Mountains
10
Meet Olympus Mons

• Compared to mountains on the Earth
• http//volcano.und.nodak.edu/vwdocs/planet_volcano
  /mars/Shields/size.html

11
Mountains in Cross-Section
12
In 3-D
13
Thats Why Stars Are Round! but Why are
They Hot?

• Self-gravity plus
• A conservation law our very first profound
  piece of physics.