Finding Normal and Tangent Vectors for a 3D Space Curve

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Discussion Overview

The discussion revolves around finding normal and tangent vectors for a 3D space curve represented by a vector function f(t). Participants explore the mathematical definitions and calculations involved in determining these vectors, focusing on the implications of parametric definitions in three dimensions.

Discussion Character

  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • Adrian asks how to find the normal and tangent vectors at any location along a 3D curve defined by a vector function f(t).
  • One participant suggests that the tangent vector at a point P is related to the direction in which P is moving, indicating the need to consider the rates of change in each coordinate direction.
  • Another participant identifies the first derivative f'(t) as the tangent vector but expresses uncertainty about defining the normal vector in this context.
  • A further contribution clarifies that for a parametrically defined function, the tangent vector can be expressed in terms of the derivatives of the component functions, but questions how to define the normal vector since it would typically be perpendicular to the tangent.
  • One participant provides a formula for the tangent vector and suggests that the normal vector can be derived from the unit tangent vector's derivative with respect to t.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the normal vector's definition and calculation, indicating that there is no consensus on how to approach this aspect of the problem.

Contextual Notes

The discussion highlights the complexity of defining normal vectors in three-dimensional parametric space, with some assumptions about the nature of the curve and the derivatives involved remaining unaddressed.

adoado
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Hello all,

Given a 3d vector function f(t) that traces out a path in space, how can I find the normal and tangent vectors at any location along the curve?

Cheers,
Adrian
 
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Well, for us to have a tangent at [itex]P(x(t_1), y(t_1), z(t_1) )[/itex] , the direction the tangent should be pointing in the same direction as the point P is "going" right at that instant when t= t_1. We could break it into dimensions and think about how fast P is going in just the x-direction, how fast it's going in the y-direction and how fast in the z-direction. How could we figure that out?
 
Right, so it would be the first derivative, or f'(t). But the normal?
 
Well there's no first derivative, you have a parametrically defined function of 3 variables. So in the x direction, its x'(t), then in y, y'(t) and in z axis, z'(t).

For the normal, I'm not sure. How would you define the normal vector in this case? Normally its the vector perpendicular to the Tangent, but we get a whole Plane that has that for this case.
 
If [itex]\vec{f}(t)= u(t)\vec{i}+ v(t)\vec{j}+ w(t)\vec{k}[/itex], then a tangent vector is given by [itex]\vec{f}'(t)= u'(t)\vec{i}= v'(t)\vec{j}+ w'(t)\vec{k}[/itex]. The unit tangent vector is that vector divided by its length and the normal vector is the derivative of the unit tangent vector with respect to t.
 

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