See previous answer:
http://www.theanswerbank.co.uk/Recently/Question51643-6.asp? Page=1
That covers much of your question. In addition, the shape of follicles vary (between different people, and between different parts of the body).
Some follicles are nearly round, and tend to produce straight hair. Others are narrow, producing ribbon-shaped hair which curls as it is extruded.
The fixed time that hair grows for is also the reason why hair seems to grow faster when cut shorter. When cut off short, you are cutting all the hairs, including those which have stopped growing, those just started, and all in between.
When you cut it longer (whether on the head or elsewhere) you are only cutting those hairs which have nearly reached their final length -- they of course are slowing down.
An interesting question is how each follicle "knows" which part of the body it's in. This is a difficult topic for developmental biology, and also applies to all other cells. Whole careers in that one...
I hope that's covered the short and curlies now....