parabola: a plane curve formed by the intersection of a right circular cone and a plane parallel to an element of the curve
entity: that which is perceived or known or inferred to have its own distinct existence (living or nonliving)
rutherford atom: first modern concept of atomic structure; all of the positive charge and most of the mass of the atom are contained in a compact nucleus; a number of electrons (equal to the atomic number) occupy the rest of the volume of the atom and neutralize the positive charge