Angular Momentum Balance

  • #1
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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
 

Answers and Replies

  • #2
haruspex
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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.
 
  • #3
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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
 
  • #4
haruspex
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how they compute the cross product
For that, I need you to define the r and u vectors in the boxed equation.
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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