Hi This is a mail in the same series as before: stresses in gas.
Admit that it is not obvious what is B and what is N in this case: http://en.wikipedia.org/wiki/Frenet-Serret_formulas Imagine the animated spring on the right to be longer and curved so that the end is attached to the beginning. In that case one can even imagine a trinormal pointing to the center of the circular spring. David David Jonsson, Sweden, phone callto:+46703000370
