Thread:Comments:Scientists say the moon is slowly shrinking/Comments from feedback form - "So it may be shrinking. Its ma..."/reply (10)

You're thinking of this backwards.

Earth's equatorial radius is currently 6,378 kilometres. If you crushed the Earth to the size of a pea, it would be a black hole. But someone orbiting from a distance of 6678 kilometres from the centre of mass (300 kilometres above the current surface, or Near Earth Orbit) would experience the same force of gravity in either circumstance. Regardless of whether you are 6678 kilometres from the centre of the Earth or 6678 kilometres from the centre of an Earth massed black hole, the gravity you experience will be identical. At a given distance from an object the force of gravity will be the same, regardless of the density of the object, provided that all the mass of the object is below you.

The reason that a black hole "has a stronger gravitational field" (even though it doesn't really) is because you can get much closer to the centre of mass without crashing into the surface. That's it.