Dot product of a vector with the derivative of its unit vector

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Homework Help Overview

The problem involves the dot product of a vector function c(t) with the derivative of its unit vector, specifically examining the expression c(t) · d/dt(c(t)/||c(t)||). The context is centered around vector calculus and properties of derivatives of unit vectors.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the derivative of the unit vector and its implications when dotted with c(t). There are inquiries about the magnitude of the unit vector and its constancy. Some participants explore the relationship between c(t) and its unit vector.

Discussion Status

There is an ongoing exploration of the properties of the unit vector derived from c(t). Some participants have provided insights that seem to clarify the relationship between the vectors involved, while others are still questioning the implications of these relationships.

Contextual Notes

Participants are working under the assumption that ||c(t)|| is non-zero and are considering the implications of this condition on their reasoning. There is also a focus on the nature of the dot product and its results in the context of constant vectors.

hoopsmax25
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Homework Statement


Let c(t) be a path of class C1. Suppose that ||c(t)||>0 for all t.
Show that c(t) dot product with d/dt((c(t))/||c(t)||) =0 for every t.


Homework Equations


I am having trouble with the derivative of (c(t)/||c(t)||) and how to show that when its dotted with c(t) that it always equals zero.


The Attempt at a Solution


I know that c(t) dotted with c'(t) =0 when ||c(t)||= a constant but don't know how to implement this fact for this problem.
 
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If d(t)=c(t)/||c(t)||, what is ||d(t)||?
 
What is the magnitude of c(t)/||c(t)||?
 
would it be 1?
 
hoopsmax25 said:
would it be 1?

Show why it is 1. Then you can drop the '?'.
 
Ok i get that now. So if d(t)=1, which is a constant, then d(t) dotted with d'(t) =0. Since c(t)/||c(t)|| has the same direction as c(t), we can then plug c(t) in for d(t). Does that make sense to do?
 
hoopsmax25 said:
Ok i get that now. So if d(t)=1, which is a constant, then d(t) dotted with d'(t) =0. Since c(t)/||c(t)|| has the same direction as c(t), we can then plug c(t) in for d(t). Does that make sense to do?

Makes sense to me.
 
Awesome. Thanks for the help
 

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