Question: What does VectorCalculus:-Curvature represent?


I'm surprised by the result of the procedure VectorCalculus:-Curvature which is always a positive scalar quantity:
For instance
c := VectorCalculus:-Curvature(<x, sin(x)>, x):
plot(c, x=0..2*Pi) 
# c >=0 for all x in [0, 2*Pi]

In the help pages it's written that the (signed) curvature for a function y(x) is y''/(1+y' 2)(3/2).

y := sin(x):
c := diff(y, x$2) / (1+diff(y,x)^2)^(3/2):
plot(c,  x=0..2*Pi) 
# c < 0 if x in (0, Pi)  and  c > 0 if x in (Pi, 2*Pi)

Could you please help me to understand this?

Thank in advance

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