Birds in a truck - I'm not getting it

  • Thread starter Graeme M
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In summary, the conversation discusses a problem where a truck with sealed walls, floor and roof and containing a flock of birds weighs the same whether the birds are in flight or at rest. This is due to the flapping of the birds' wings which causes a downwards force equal to their weight. The total mass of the system remains constant, but the operational weight (OW) varies as the birds are aloft, leading to a reduced OW while they are flying. This may differ from the gravitational weight (GW) which is a fixed value and not directly measurable. The conversation also mentions different definitions of weight and how they relate to the problem.
  • #71
The mentors have discussed and the thread will remain closed. The correct physics has been explained and now the thread is just going in a circle and heading towards personal speculation.

Graeme M said:
The detail is critically important. At least to me.
The question is which details are important? Do you think that the color of the box makes a difference? Or perhaps whether the box is arranged with the length north/south vs. east/west? Perhaps you should worry about different types of birds, maybe pigeons vs. doves, or maybe different colors of the same species?

For any physical scenario there are important details and there are unimportant details. For this scenario there is only one detail which is important, the vertical acceleration of the center of mass of the system (truck plus contents). All other details are unimportant. Given the GW of the system and given the vertical acceleration of its COM you can immediately find the OW, regardless of any other details.
 
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  • #72
The thread will remain closed.

@Graeme M -- Please do some more reading about aeronautics to help your understanding of the things you were told in this thread. After you have done some reading, if you have specific questions about what you have read, please feel free to post in the Engineering/Aeronautics forum here on the PF. Posts like "I believe this, how am I wrong" are not generally permitted here on the PF. Specific questions about things you have read at credible websites certainly are allowed.
 
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