Not sure the precise concept of "normal observation", but I assume that is observed by "eyes".
Eye observation is basically macroscopic, but when you use a mark, which can be regarded as a point of mass, then it goes to microscopic.
Mark is a reference point which you can compare the relative position change, but with your eyes, first you cannot notice microscopic changes, second the eyes cannot precisely set a stable reference point.
They should be bigger as if it is hot the tracks will expand as it is made of metal and then there is more room for it to expand or contract
Answer:
r is the separation between the two spherical bodies
I would expect it to be slightly basic.
