# A Theory of Surfaces and Theory of Curves Relationship

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1. Nov 14, 2016

### ltkach2015

Hello

I am interested in the Frenet-Serret Formulas (theory of curves?) relationship to theory of surfaces.

1) Can one arrive to the Frenet-Serret Formulas starting from the theory of surfaces? Any advice on where to begin?

2) For a surface that contain a space curve: if the unit tangent vector to the curve is the very same unit tangent vector the surface then why/how is the unit normal vector to the curve not in the same direction as the surface's gradient vector?

Thank you

2. Nov 14, 2016

### lavinia

A basic book on classical differential geometry is Lectures on Classical Differential Geometry by Struik. Without a specific question it is difficult to give a specific reply.

3. Nov 16, 2016

### ltkach2015

Ok

Why doesn't the normal to space curve contained on a surface not point in the same direction as that surfaces normal vector (gradient)?

4. Nov 16, 2016

### zinq

Think about latitude circles on a sphere.

5. Nov 18, 2016

### ltkach2015

Oh ok!

So the sphere's gradient vector would point in the same direction as the circle's negative normal vector?

6. Nov 18, 2016

### zinq

Hint: You can determine the circle's normal vector from the plane that it's in.