Gravity is an attraction between objects with mass. Its effect grows weaker as their separation increases; crossing the edge of the atmosphere does not switch it off. Gravity is central to how moons and planets move.
How distance changes gravity
In our idealised Earth model, gravitational acceleration follows g = μ / r². Double the distance from Earth's centre and the acceleration becomes one quarter as large. The reference is distance from the centre, not height above the ground.
You can calculate a comparison without memorising a table. At a height equal to one Earth radius, the distance from the centre is two Earth radii. The model therefore gives one quarter of its surface acceleration.
Gravity and orbit describe different things
Gravity describes the attraction. Orbit describes a trajectory. In the lab, keep the altitude fixed and adjust speed: the gravitational field at the starting position stays the same while the predicted path changes.
Explore motion and gravity →
These comparisons use a spherical, isolated Earth. Real gravity fields are more complicated, and this simple model is not a mission-planning tool.
Sources & model notes
Diagrams are explanatory illustrations. EXOVAS is independent and is not affiliated with NASA or JPL.