Gravity

1. Gravity

2. Gravitational Field Interpretation: Gravitational Field is the force that a test particle would feelat a point divided by the mass of the test particle. Why bother?

3. Newtonian View vs. Fields Newtonian Mechanics Action at a Distance Fields Local interactions All particles generate fields; test particle interacts with local field.

4. Fields Fields: • Can have finite propagation speeds (static fields are long time consequences of dynamics fields). • Can store and transmit energy and momentum. • Are needed for relativistic quantum mechanics and dynamics. • Are needed for general relativity and gravitational radiation.

5. Now we can use Gauss’s Law to calculate g. Gravitational Field

6. Gauss’s Law Spherically symmetric system:

7. Gravity Field Field Density Inside constant density: Decreases like r Outside: Increases like 1/r2

8. Constant Density Sphere Field Density Inside: Outside:

9. Wall g g A A A

10. z0 R Field from Direct Integration

11. z0 R Limits If z0 >> R: Like a point mass! If z0 << R: Like a wall of mass!