Analysis of a deformable body and Newton's 3rd Law

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Discussion Overview

The discussion revolves around the application of Newton's 3rd Law in the context of deformable bodies, particularly focusing on how forces interact across surfaces of a solid under deformation. Participants explore the implications of static equilibrium and the nature of forces acting on different surfaces within a solid, referencing concepts from mechanics and theoretical physics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how Newton's 3rd Law applies when deformation occurs, citing A.P. French's assertion that reaction forces involve deformation.
  • Another participant states that in a static frame, the net forces on any sub-portion of a solid must sum to zero, implying traction forces across surfaces must balance.
  • Concerns are raised about how to demonstrate that forces on the positive and negative x-surfaces are equal, despite both being unaccelerated.
  • It is suggested that the positive x-surface is influenced by forces from the negative x-surface, leading to a discussion on the nature of these interactions.
  • Participants discuss the concept of free body diagrams and how they illustrate the balance of forces acting on a body.
  • There is a mention of the need for internal stresses within the cube to counteract external forces, with a focus on the point-wise balance of these forces.
  • One participant expresses confusion regarding the implications of forces vanishing and the relationship between stationary bodies and elongation.
  • A later reply suggests analyzing the situation at a molecular level to understand the similarities with Newton's laws.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and agreement regarding the application of Newton's 3rd Law in the context of deformable bodies. There is no consensus on how to definitively demonstrate the equality of forces across surfaces, and the discussion remains unresolved with multiple competing views on the nature of these forces.

Contextual Notes

Limitations include the complexity of the arguments surrounding the application of Newton's laws in deformable bodies, the dependence on definitions of forces and equilibrium, and the unresolved nature of how deformation affects force interactions.

  • #31
Paul Colby said:
The part where the forces on my bottom vanish, apparently.
The vertical surface doesn’t have a bottom?
 
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  • #32
Chestermiller said:
The vertical surface doesn’t have a bottom?
Who said I was slouching?
 

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