$6.[$Sec$.10\mathrm{.}8]$ The torsion, $,$ measures the degree of twisting of a curve and can be computed from

$=[$r$($t$)$ r$($t$)]$ r$($t$)$

$||$r$($t$)$ r$($t$)||2$

Find the torsion of the curve r$($t$)=$a cos t$,$ a sin t$,$ bt$$ where a $>0$ and b $>0.($Although we are not considering a parallelepiped

here, this is a sweet application of the scalar triple product$).$ Interesting fact: curves with zero torsion lie in planes.