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Re: Curvature for a circle

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  • Subject: [mg83115] Re: Curvature for a circle
  • From: "Steve Luttrell" <steve at>
  • Date: Sun, 11 Nov 2007 03:02:20 -0500 (EST)
  • References: <fh3qqc$o9$>

This looks like a homework question, so I will limit my response to hints:

Have a look at the Wikipedia page on curvature at, where you will see an expression for 
curvature \[Kappa] in the plane defined in terms of (derivatives) of y[x]. 
The rest is up to you to do.

Steve Luttrell
West Malvern, UK

<dpdoughe at> wrote in message news:fh3qqc$o9$1 at
> It can easily be shown that the curvature for a circle of radius r is
> 1/r.  How can I get Mathematica to show me this?
> I have defined a function to calculate the curvature for me assuming a
> vector-valued function.
> Curvature =
>  Function[{V, x}, Norm[D[D[V, x]/Norm[D[V, x]], x]/Norm[D[V, x]]]];
> S = {2*Cos[theta], 2*Sin[theta]}
> ListPlot[Table[{t, Curvature[S, theta] /. theta -> t}, {t, 0, 2*Pi}]]
> I don't get anything for a plot.  If I look at what my curvature
> formula calculates for me there are some questions as to if
> Abs'  (Derivative of absolute value??) being left unevaluated.
> Any thoughts?  It should be a straight-forward calculation....

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