1. Two Body Orbits (M + m)P2 = a3 It does! Center of Mass
How come the Sun doesn’t go around the Earth?
It does!
Center of Mass
The Center of Mass is where the two masses would balance
The objects go around each other
(M + m)P2 = a3

2. Applies to planets around the Sun
Kepler Vs. Newton
Applies to planets around the Sun
P2 = a3
(M + m)P2 = a3
Always applies
Masses in Solar Masses
Sun + Earth
M + m =
 1

3. Gravity Vs. Pressure = Sphere
Gravity wants to squish everything to a point
Pressure wants it to spread out
They balance to make a sphere
If an object rotates, it makes a flattened (oblate) sphere
Small objects can be any shape

4. Precession
Gravity pulls unevenly on the flattened Earth
Earth is like a top – its tilt changes over time
26,000 year cycle

5. Gravity vs. Rotation = Disk
Dust or gas or chunks - disk forms
Rotation keeps it from falling in
Gravity keeps it from escaping
Rings around Planets
Spiral Galaxies
Accretion disks
Protoplanetary disks

6. Tidal Forces

7. Q. 11: How Often Do Tides Occur?
Tidal Distortion
Greatly Exaggerated
Q. 11: How Often Do Tides Occur?

8. Spring (Big) and Neap (Small) Tides
Big Tides
Small Tides

9. Bulges and the Earth/Moon System
with rotation
without rotation
Earth
Earth
Moon
Q. 12: Tidal Locking
Earth and Moon bulge want to align
Strong effect on the Moon
Rotation causes bulge to be in wrong place
Bulge has gravitational pull on Moon
Earth rotation slows
Moon slung to higher, slower orbit

10. Tidal Locking
Moon
Earth
Moon
Moon
Moon

11. Tidal Heating planet moon Changing shape as distance changes
Flexing generates heat
planet
moon

12. Roche Limit
Planet
Moon

13. Q. 13: Titan and Tidal Forces
Roche Limit - Rings
Q. 13: Titan and Tidal Forces

14. Light and Other Electromagnetic Waves
Energy
Energy is ability to do work
Energy comes in many forms
Energy can change forms
Nuclear
Heat
Light
Chemical
Kinetic (motion)
Gravitational
Heat

15. Some Types of Energy Kinetic Energy – Energy of motion
Heat is actually kinetic energy
Electric and Magnetic Energy
Light is a kind of electromagnetic energy
Gravitational
When two objects are far apart, they have a lot of gravitational energy
Nuclear energy
Powers the Sun and stars