Understanding Free Body Diagrams: Explaining the Forces on a Compressed Board

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Homework Help Overview

The discussion revolves around understanding free body diagrams in the context of a board compressed between two other boards. The original poster expresses confusion regarding the forces acting on the middle board, particularly questioning the omission of certain forces in a provided solution manual diagram.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the distinction between normal and compression forces, with some questioning whether they should be considered separate entities. The original poster presents their interpretation of the free body diagram, while others seek clarification on the reasoning behind the solution manual's representation.

Discussion Status

The discussion is active, with participants providing feedback and engaging in a dialogue about the nature of the forces involved. There is an acknowledgment of differing interpretations regarding the forces acting on the middle board, and some participants express appreciation for the feedback received.

Contextual Notes

There is a mention of friction being present between the boards, which may influence the forces at play. The original poster also notes a discrepancy between their understanding and the solution manual's diagram.

Romain Nzebele
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Hello everyone. I find the following problem confusing.

A board sandwiched between two boards in the figure below weighs 95.5N. If friction exists between the middle and the compressing boards, draw the free body diagram of the middle board.

Below I attached the diagram found in the solution manual but I don't agree with it. Since the middle board is compressed by 2 boards, I believe the diagram should include two forces pointing toward the middle board in addition to the normal forces. Can someone explain to me why the solution manual omitted them? I will appreciate it very much.
 

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Please show us your version of the free body disgram.
 
Hello, here is the body diagram I believe is correct. In my drawing Ff represents the force of friction, F represents the compression force, N represents the normal force, and Fg represents the weight of the middle board.
 

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What makes you think that N and F are separate and distinct entities? Why isn't the normal force N just the compression force F?
 
The normal force results from the compression force. If there was no compression force, there will be no normal force. Since we have two boards compressing the middle block, it seems correct to me to represent these forces. Although I understand that the normal force and the compression force are equal in magnitude in this example.
 
Romain Nzebele said:
The normal force results from the compression force. If there was no compression force, there will be no normal force. Since we have two boards compressing the middle block, it seems correct to me to represent these forces. Although I understand that the normal force and the compression force are equal in magnitude in this example.
There is only one force. You can call it a compression force or you can call it a normal force, but either way, there is only one. They are one and the same thing.
 
Okay, thank you for the feedback. I appreciate it.
 
Romain Nzebele said:
Okay, thank you for the feedback. I appreciate it.
My pleasure. By the way, Welcome to Physics Forums!
 

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