What went wrong in calculating the curvature for r(t)=<t^2,lnt,tlnt>?

  • Thread starter Thread starter bl4ke360
  • Start date Start date
  • Tags Tags
    Curvature
Click For Summary
SUMMARY

The discussion centers on the calculation of curvature for the vector function r(t) = . The correct curvature formula is k(t) = |r'(t) x r''(t)| / |r'(t)|^3, which yields a result of 0.3, contrasting with the incorrect calculation that resulted in 0.4. The error was identified in the normalization of the tangent vector T(t); specifically, the user incorrectly used |r'(1)| instead of |r'(t)|, leading to inaccuracies in T'(t) and ultimately affecting the curvature calculation.

PREREQUISITES
  • Understanding of vector calculus, specifically curvature calculations.
  • Familiarity with the concepts of tangent vectors and their normalization.
  • Knowledge of cross products in three-dimensional space.
  • Proficiency in differentiating vector functions.
NEXT STEPS
  • Review the derivation of curvature formulas in vector calculus.
  • Study the process of normalizing vectors, particularly in the context of T(t).
  • Learn how to compute cross products and their applications in curvature.
  • Practice differentiating vector functions to solidify understanding of T'(t) and its implications.
USEFUL FOR

Students studying vector calculus, particularly those tackling problems related to curvature, as well as educators seeking to clarify common mistakes in vector normalization and differentiation.

bl4ke360
Messages
19
Reaction score
0

Homework Statement



r(t)=<t^2,lnt,tlnt>

Homework Equations



k= |T '(t)| / |r '(t)|

The Attempt at a Solution



2llfsyu.jpg



My professor's answer sheet solved the problem using the other method, k(t)=|r '(t) x r ''(t)| / |r '(t)|^3
and that answer ends up being 0.3, while mine is 0.4. I can't see where I made any mistakes, and why I got 9 points marked off. Can someone explain?
 
Physics news on Phys.org
bl4ke360 said:

Homework Statement



r(t)=<t^2,lnt,tlnt>

Homework Equations



k= |T '(t)| / |r '(t)|

The Attempt at a Solution



2llfsyu.jpg



My professor's answer sheet solved the problem using the other method, k(t)=|r '(t) x r ''(t)| / |r '(t)|^3
and that answer ends up being 0.3, while mine is 0.4. I can't see where I made any mistakes, and why I got 9 points marked off. Can someone explain?

Yes. T(t) is supposed to be a unit vector for any value of t. You normalized it so that |T(1)|=1. But it's not a unit vector for any t. So your T'(t) comes out wrong.
 
I think what you did wrong was when you calculated T(t), you plugged in |r'(1)| in the denominator, when you should have left it as |r'(t)| until after you differentiated T(t) to get T'(t). By doing this you lost the terms related to changes in |r'(t)|. Does this make sense?
 

Similar threads

  • · Replies 22 ·
Replies
22
Views
7K
Replies
1
Views
1K
  • · Replies 3 ·
Replies
3
Views
11K
  • · Replies 5 ·
Replies
5
Views
2K
Replies
5
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K