Proving derivatives of a parametrized line are parallel

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Homework Help Overview

The discussion revolves around proving that the second derivative of a parametrized line, σ''(t), is parallel to the first derivative, σ'(t). The context involves understanding the properties of derivatives in relation to vector functions that represent lines.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the parametrization of a line, questioning whether σ(t) can be expressed in different forms and what implications this has for the derivatives. There is a discussion about the nature of parallel vectors and the conditions under which they can be considered parallel.

Discussion Status

The conversation includes attempts to clarify the definitions of the vectors involved and their roles in the parametrization of a line. Some participants express uncertainty about the implications of constant velocity and the relationship between the derivatives.

Contextual Notes

Participants are considering different forms of parametrization and the assumptions that come with them, such as the nature of direction and position vectors. There is an acknowledgment that both direction and position vectors are constants in this context.

V0ODO0CH1LD
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Homework Statement



Show that if σ(t) for (t in I) is a parametrization of a line, then σ''(t) is parallel to σ'(t).

Homework Equations





The Attempt at a Solution



I thought that if σ(t) is a parametrization of a line then it could be expressed as σ(t) = vt + a, but then σ'(t) = v and σ''(t) = 0. Can two vectors be parallel? Is it because the distance between them is constant? Or did I make a mistake earlier on?
 
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V0ODO0CH1LD said:

Homework Statement



Show that if σ(t) for (t in I) is a parametrization of a line, then σ''(t) is parallel to σ'(t).

Homework Equations





The Attempt at a Solution



I thought that if σ(t) is a parametrization of a line then it could be expressed as σ(t) = vt + a, but then σ'(t) = v and σ''(t) = 0. Can two vectors be parallel? Is it because the distance between them is constant? Or did I make a mistake earlier on?

That would be the equation of a line where the point ##\sigma(t)## moves with constant velocity. But what about something of the form ##\sigma(t) = f(t)\vec D + \vec a##? Wouldn't that give a straight line too?
 
Ah, thank you! But both ##\vec{D}## and ##\vec{a}## are still just regular vectors, right?
 
V0ODO0CH1LD said:
Ah, thank you! But both ##\vec{D}## and ##\vec{a}## are still just regular vectors, right?

Yes. ##\vec D## is a direction vector and ##\vec a## is a position vector to a point on the line. Both vectors are constants.
 

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