Some life forms move so slowly that their movement can not be detected by normal observation the best way to determine any movement is by placing a mark at some point, and observing any change in position from it. why is this true

because the form can be watched over a long time for deviations from the mark.

like fingernails, the grow slowly too. after a time, they get clipped

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.