15.) Thus the fibres half-way between the neutral plane and the outer surface experience only half as much shortening or elongation as the outermost or extreme fibres.
Similarly for other distances.

The elements along the neutral plane experience no tension or compression in an axial direction.

The line of intersection of this plane and the plane of section is known as the ~neutral axis~ (N A in Fig.

15) of the section.
[Footnote 9: While in reality this relationship does not exactly hold, the formulae for beams are based on its assumption.] [Illustration: FIG.

15 .-- Diagram of a simple beam.