I am asked to "Define the following in terms of bending theory" and i am strugling to find information in the depth i need.

Neutral axis: all i know about this is it is a cross section of a beam perpendicular ot its longitudianl axis, and that on one side of the axis the fibres are in a state of tention and on the other a state of compression. Any ideas on how i can extend this or were i can find information?

Radius of curvature: All i know about this is normally the beam does not bend into circular arc, but whatever shape the beam takes under the sideways loads, it will basically form a curve on an x –y graph.

Moments of resistance:The fibres above the neutral surface are in compression and those below the neutral surface are in tension. (any ideas on how i can expand this?)

Section modulus: Section modulus of a beam is the ratio of a cross section's second moment of area to its greatest distance from the neutral axis.

Am i on the right lines with these and does anybody know how i can expand on them.