14.4. Normal Curvature and the Second Fun- damental Form
14.4. Normal Curvature and the Second Fun- damental Form
14.4. Normal Curvature and the Second Fun- damental Form
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Observe that −→ n g is <strong>the</strong> unit normal vector to <strong>the</strong> curve C<br />
contained in <strong>the</strong> tangent space T p (X) at p.<br />
<strong>Normal</strong> <strong>Curvature</strong> . . .<br />
Geodesic <strong>Curvature</strong> . . .<br />
If we use <strong>the</strong> frame ( −→ t , −→ n g , N), we will see shortly that<br />
X ′′ (s) = κ −→ n can be written as<br />
κ −→ n = κ N N + κ g<br />
−→ ng .<br />
The component κ N N is <strong>the</strong> orthogonal projection of κ −→ n onto<br />
<strong>the</strong> normal direction N, <strong>and</strong> for this reason κ N is called <strong>the</strong><br />
normal curvature of C at p.<br />
The component κ g<br />
−→ ng is <strong>the</strong> orthogonal projection of κ −→ n onto<br />
<strong>the</strong> tangent space T p (X) at p.<br />
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We now show how to compute <strong>the</strong> normal curvature. This will<br />
uncover <strong>the</strong> second fun<strong>damental</strong> form.<br />
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