Formula: $g_d$ = g(1 - d/R) (exact, assuming uniform density)

This is a LINEAR decrease. At the centre (d = R): g = 0.

Physical reasoning: At depth d, only the sphere of radius (R-d) below contributes to gravity (shell theorem: the outer shell produces zero net field inside).

Comparison with height:

• Height: g decreases as 1/$r^2$ (faster initially, then slows down)
• Depth: g decreases linearly (constant rate)
• At the same small distance delta from the surface: g decreases faster with height (2*delta/R > delta/R)