Rune Skovbo Johansen
I learned yesterday that the falloff of gravity for a spherical mass is exactly the same as for a point mass outside of the mass, and just reduces linearly to zero at the center inside the mass.
This was surprising to me; I wouldn't have expected such a non-smooth function.
(This assumes a uniform distribution of mass of course, which Earth does not have.)
@runevision oh that's interesting indeed, I first thought this would be a fairly straight standard thing but colour me surprised
@runevision Another (possibly related) fact is that if you want to remove 25% of the surface area of a sphere you only need to cut through at a plane that's half the radius away from the centre, i.e. one that from a 2D perspective is 25% up the sphere. I reckon this and your gravity one come down to similar maths.
@runevision This is because the gravity field anywhere inside a sphere (due to the sphere) is zero - all the directions cancel each other out.
The gravity field of a sphere you're not inside is as if all the mass is at the center.
So as you travel out, all you're feeling is the sphere "below" you, which is increasing in mass according to r^2, but also its center is getting further away by r. Divide one by the other = linear.
It's neat that two simple-but-surprising results give a third.