Euler equations in rigid body: Taylor VS Kleppner - Kolenkow

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Discussion Overview

The discussion centers on the interpretation of Euler equations in rigid body motion as presented in two different textbooks: Kleppner - Kolenkow and Taylor. Participants explore the physical meaning of these equations, particularly regarding the frames of reference used in their derivation and application.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant notes that Kleppner - Kolenkow describes Euler equations in the context of an inertial frame, while Taylor presents them in the context of a body-fixed frame, leading to confusion about their equivalence.
  • Another participant suggests that if the equations were in the body frame, the angular velocity (ω) would be zero, indicating a potential misunderstanding in the interpretation of the frames.
  • A different participant asserts that the Euler equations are indeed formulated in a non-inertial frame that moves with the body.
  • One participant expresses concern that Kleppner - Kolenkow may not explain the concepts clearly, suggesting a possible error in their presentation.
  • A participant offers a link to their manuscript in German, which details the relations between the body and inertial frames, implying that it may provide further clarification.

Areas of Agreement / Disagreement

Participants express differing interpretations of the frames of reference in the Euler equations, with no consensus reached on whether one textbook is correct over the other. The discussion remains unresolved regarding the clarity and accuracy of the explanations provided in the texts.

Contextual Notes

Participants highlight the differences in the approaches taken by the two textbooks, including the use of vector methods and the small angle approximation in Kleppner - Kolenkow versus the relation between inertial and non-inertial frames in Taylor. These differences contribute to the confusion surrounding the physical meaning of the Euler equations.

almarpa
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Hello all.

After reading both chapters on rigid body motion both in Kleppner - Kolenkow and Taylor books, I still do not undertand the physical meaning of Euler equations. Let me explain:

In Kleppner - Kolenkow, they claim (page 321 - 322) that in Euler equations, Γ1, Γ2 and Γ3 are the components of the torque as viewed in the inertial (space) frame at some time t, ω1, ω2, ω3 are the components of angular velocity in that same frame, and dω1/dt, dω2/dt, dω3/dt the instantaneous rate of change of those components. Thus, Euler equations relate all these quantities in the inertial space frame at time t.

On the other hand, in page 396, Taylor says that the Euler equations determine the motion of a spinning body as seen in a frame fixed in the body (so I guess he means, as seen in the body frame). So Γ1, Γ2 and Γ3, and ω1, ω2, ω3, are the componnetes of torque and angular velocity in the rotating body frame.

As you see, I am really confused. Besides, to derive Euler equations, Kleppner - Kolenkow use a vector approach and the small angle approximation, while Taylor uses a relation between inertial and non inertial frames, which I have nor studied yet, and maybe this is the source of my confusion.

Are they the same statement, but explained in diffrents ways? If so, I do not understand it.

Is any of the explanations wrong? If so, which is the correct one?

Thanks a lot for your help.
 
Last edited:
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Hi
I'm not sure, but i guess they mean the inertial frame of referece. If they meant frame of the body, ω would be zero as well as ∝. But you should wait for an answer of someone more experienced :)
 
The Euler equations are in the non-inertial frame comoving with the top (body frame).
 
Thanks for your reply. That is what I thought, too.

Then, there must be a mistake in Kleppner - Kolenkow's book (or, at least, they do not explain it properly, because that is what I understood after reading that section).
 
Unfortunately my manuscript on mechanics is in German. There I worked out the relations between the body and inertial frame in detail. Perhaps you can understand it, because there are many formulae:

http://theory.gsi.de/~vanhees/faq/mech/node73.html

or in pdf

http://theory.gsi.de/~vanhees/faq-pdf/mech.pdf
 
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