13.1.2—A gravitational field by means of field lines

A field line points in the direction of force on a small positive test mass; closer lines represent a stronger field qualitatively.

Lines are a visual model, not physical tracks. Around an isolated mass they point radially inward and do not cross.

Parallel equally spaced lines model an approximately uniform field near Earth’s surface; radial lines model a point mass.

Field-line density is not an exact numerical scale, and crossing lines would imply two field directions at one point.