How Is Angular Momentum Calculated Without Considering Gravity and Viscosity?

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Homework Help Overview

The discussion revolves around the calculation of angular momentum in a scenario where gravity and viscosity are neglected. Participants are trying to understand the derivation of an equation presented in an image related to this topic.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants express confusion regarding the setup of the problem, particularly the altitude and the angle of the variable ##b_1##. There are inquiries about the force from the plate and how to define the vectors involved in the cross product calculation.

Discussion Status

The discussion is ongoing, with participants questioning the assumptions made in the problem setup and seeking clarification on specific components of the equation. Some guidance has been offered regarding the nature of the forces involved, but no consensus has been reached.

Contextual Notes

Participants note that the problem is idealized, and there is a lack of information regarding the center of the force from the plate, which complicates the analysis of torque.

Est120
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Homework Statement
write the macroscopic angular momentum balance for the following problem
Relevant Equations
see image
we neglect gravity and viscosity efects
i really can't understand how does the author managed to get the equation in the image
Bird Angular Momentum Balance.png
 
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Not making any sense to me either.
Altitude at ##\frac 12b_1## from where?
##b_1## is at an angle, so ##b_1-b_{2a}## doesn’t seem right.
And what about the force from the plate? We don't know where that is centred, so we can't set the axis so as to eliminate its torque.
 
it's an idealized problem, all i need to know is how they compute the cross product , there is no viscosity so there is no friction with the plate
 
Est120 said:
how they compute the cross product
For that, I need you to define the r and u vectors in the boxed equation.
Est120 said:
there is no friction with the plate
It's not to do with friction. The incoming flow exerts a vertically downward force ##w_1v_1## on the plate. The reaction from the plate likely has a torque about the chosen axis.
 

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