Newtonian gravity

• Why Does Gravity Hold the Planets in Orbit if Electric Forces Are Stronger?
  Electric forces between particles can dwarf gravity, but stars and planets are nearly neutral; their mass adds up, so gravity governs their orbits.
• What Is the Divergence of the Gravitational Field?
  In Newtonian gravity, the divergence of the gravitational field is -4πGρ; it vanishes in empty space and is singular at point masses.
• Is Gravity 9.8 m/s² at Every Height?
  Gravity is about 9.8 m/s² near Earth's surface, but decreases with altitude according to the inverse-square law; learn when the approximation works.