1. Chapter 9: Gravity
Gravity is the force most familiar to us, and yet, is the least understood of all the fundamental forces of nature.

2. Four Fundamental Forces of Nature
Gravity
Electromagnetism
Strong Nuclear Force (This holds atomic nuclei together)
Weak Nuclear Force (Allows for radioactive decay)

3. Kepler’s Three Laws of Planetary Motion
Go Columbia!!
Johannes Kepler ( )

4. First Law
Each planet moves in an elliptical orbit with the Sun at one focus.

5. An Ellipse Foci r1+r2 = constant a Minor Axis r2 r1
Semi-major Axis (a)
Major Axis

6. Orbiting planet
Sun at one focus

7. The Second Law
The line from the sun to any planet sweeps out equal areas in equal times.

8. Orbiting planet A A
Sun

9. The Third Law
The square of the orbital period is proportional to the cube of the semi-major axis
For a circular orbit, the semi-major axis is the radius

11. Newton’s Law of Universal Gravitation
Every body in the universe exerts a force on every other body which is proportional to the product of their masses and inversely proportional to the square of the distance between them

13. R M1 M2

15. The Tides

17. Einstein’s Theory of Gravity

18. a =g
a =g/2
a = 0
a =g/2
a =g