Calculate the gravitational force between any two masses using Newton's law of universal gravitation. Works for planets, stars, or everyday objects.
Every object in the universe with mass attracts every other object with mass. This is Newton's law of universal gravitation, published in 1687. The force is always attractive — it pulls masses together, never pushes them apart.
The distance term is squared in the denominator, which means gravitational force drops off rapidly with distance. If you double the distance between two objects, the gravitational force becomes four times weaker. Triple the distance, and it becomes nine times weaker.
Astronauts on the ISS are NOT outside Earth's gravity — at 408 km altitude, gravity is still about 90% as strong as on the surface. They feel weightless because they are in free fall — constantly falling toward Earth, but moving sideways fast enough to keep missing it.