Question about Cartesian Tensors

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Discussion Overview

The discussion revolves around the properties of Cartesian tensors, specifically focusing on the conditions under which a certain equation (I-10) equals 1 or 0 based on the indices involved. The scope includes theoretical aspects of tensor mechanics and mathematical reasoning related to tensor equations.

Discussion Character

  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant questions why equation I-10 equals 1 when k equals i and 0 when k does not equal i.
  • Another participant provides a specific case involving the values of ##x'_0, x'_1, x'_2## to illustrate how the terms contribute to the sum in equation I-9, leading to the formulation of equation I-10.
  • A participant mentions that "a" is defined as shorthand for the cosine function, suggesting a relationship involving cosine terms in the context of the equations discussed.
  • Another participant clarifies that the indices ##i, j, k## are not related to the cosine function but are simply indices used in the equations.

Areas of Agreement / Disagreement

The discussion contains multiple viewpoints regarding the interpretation of the equations and the definitions of terms, indicating that there is no consensus on the understanding of the relationship between the indices and the equations presented.

Contextual Notes

Participants reference specific equations (I-9 and I-10) and their conditions without providing complete definitions or derivations, which may limit understanding of the context and assumptions involved.

Worn_Out_Tools
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I am not a mathematician but an Engineer-in-Training studying mechanics. That being said why does equation I-10 equal 1 when k equals i and 0 when k does not equal i?

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Worn_Out_Tools said:
I am not a mathematician but an Engineer-in-Training studying mechanics. That being said why does equation I-10 equal 1 when k equals i and 0 when k does not equal i?
Consider the case of ##x'_0=1, x'_1=0, x'_2=0##. In this case, only the terms with ##k=0## contribute to the sum in the eqn. I-9, which becomes ##x'_i=a_{ij}a_{0j}##. For ##i=0## it becomes ##1=a_{0j}a_{0j}##, for ##i=1## it becomes ##0=a_{1j}a_{0j}##, etc. For all combinations of ##k## and ##i##, you get the eqn. I-10.
 
Last edited:
“a” is defined as shorthand for the cosine function earlier in the book. So 1 = cos(0,j) * cos (0,j)?
 
Worn_Out_Tools said:
“a” is defined as shorthand for the cosine function earlier in the book. So 1 = cos(0,j) * cos (0,j)?
No. ##i, j, k## are indices.
 

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