Gravity… again

1. Gravity… again Solar System Astronomy Chapter 10

3. More than Kepler’s Laws • Gravity moves beyond orbital motion • Internal forces • Tides • Orbital resonances • Chaotic orbits

4. Internal Forces • Gravity works on every part of every body. • Therefore self-gravity exists inside a planet • This produces internal forces. These hold the planet together • There’s a special case: spherically symmetric bodies. • Force from a spherically symmetric body is the same as from a point mass at the center

5. Tidal Forces • Tides are a consequence of gravity • Consider Earth and Moon: • Parts of the Earth are closer to the Moon than other parts • The force of gravity is stronger on the closer parts

6. Tidal Forces • Tides are a consequence of gravity • Consider Earth and Moon: • Parts of the Earth are closer to the Moon than other parts • The force of gravity is stronger on the closer parts

7. Tidal Forces

8. Tidal Forces • Not until Newton could forces be analyzed • Galileo tried • Ocean’s have tidal bulge • Elongated in direction nearly pointed at Moon • (Earth rotates under tidal bulge) • Two high and low tides per day • As we are under, then opposite, the Moon • There are both lunar tides and solar tides

9. Tidal Forces • Not until Newton could forces be analyzed • Galileo tried • friction of ocean with Earth slows rotation • day grows by 0.0023 s per century • 900 million years ago – 18 hour days • tidal flexing within moon dissipated rotational motion • tidal locking • Moon being pulled forward (sped up) • 4 cm farther away each year

10. Roche Limit • aka tidal limit