1.4. Henry Cavendish calculated the value of G as 6.673×10^-11 N m²/kg²
1.5. It is important cuz it successfully explained: i) force binding us to Earth ii) motion of moon around Earth iii) planetary motion iv) tides due to Sun and Moon
2. Kepler's Laws of Planetary Motion
2.1. 1. Orbit of a planet is elliptical
2.2. 2. Line joining planet and sun is a line that sweeps equal areas in equal intervals.
2.3. 3. r³/T² = constant
2.4. *Velocity increases near Sun and vice-versa.
2.5. *Kepler couldn't give a theory to explain planetary motion.
