ASTR 20 Lecture Notes - Lecture 21: The Moons, Escape Velocity, Orbital Period
Document Summary
The force decreases by a factor of 9. Kepler"s laws had been known for 70 years, but no one knew why they worked until. Newton extended kepler"s laws as follows: kepler"s first two laws apply to all orbiting objects, not just planets, ellipses are not the only orbital paths. If a small object orbits a larger one and you measure the orbiting object"s orbital period and average orbital distance, then you can calculate the mass of the larger object. Total orbital energy= gravitational energy + kinetic energy. Total orbital energy stays constant if there is no external force. If an object gains enough orbital energy, it may escape (change from a bound to unbound orbit) Escape velocity from earth= 11 km/s from sea level (about 40,000 km/hour) Escape and orbital velocities don"t depend on the mass of the cannonball. **see phone for equation of escape velocity. The moon"s gravity pulls harder on near side of earth than on far side.
