If |p̅ (s)| is a non-zero constant, then direction of \(\frac{{{\rm{d}}\overline {\rm{p}} }}{{{\rm{ds}}}}\) is:
1
perpendicular to direction of p̅(s).
2
parallel to direction of p̅(s).
3
always makes acute angle with p̅(s).
4
it can have any direction.