13.4.2—Φ = –GM / r for the gravitational potential in the field due to a point mass

For a point mass, gravitational potential Φ is work done per unit mass from infinity and equals Φ=−GM/r.

The negative sign reflects attraction: moving a mass inward releases energy, while moving it outward requires work. Use centre distance r.

At twice the distance from a planet’s centre, potential is half as negative and closer to zero.

Potential is not the same as field strength g; Φ can be negative while g is a positive magnitude directed inward.