Do Multiple Reaction Forces Create Infinite Chains in Newton's Third Law?

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SUMMARY

This discussion clarifies misconceptions regarding Newton's Third Law of Motion, particularly in the context of multiple bodies interacting on a frictionless surface. When Body A exerts a force F(AB) on Body B, Body B exerts an equal and opposite force F(BA) back on Body A. However, the forces between multiple bodies do not create infinite reaction forces; instead, each interaction is limited to action-reaction pairs. For three bodies A, B, and C, while A pushes B with F(AB), B does not necessarily push C with the same force, and the forces between B and C are not action-reaction pairs.

PREREQUISITES
  • Understanding of Newton's Third Law of Motion
  • Familiarity with Newton's Second Law of Motion
  • Basic knowledge of frictionless surfaces in physics
  • Concept of action-reaction force pairs
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  • Study the implications of Newton's Third Law in multi-body systems
  • Explore examples of forces on frictionless surfaces in physics
  • Learn about force diagrams and free-body diagrams
  • Investigate the relationship between Newton's Second and Third Laws
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AmrD
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I have a 2 questions regarding Newton’s third law and I will explain them using examples:

1. Body A is pushing against Body B with a force F(AB), Now body B will push against body A with a reaction force F(BA) equal but opposite to F(AB). Now shouldn’t be another reaction force F2(AB) due to the action of the reaction force F(BA) and another reaction force F2(BA) as a reaction to that reaction !

2. Three bodies A, B and C setting on a frictionless surface in the order A, B and C. A is pushing on B with F(AB)
First, is it true that B will also push on C with the same force F(AB) and if that is true shouldn’t C also exert a reaction force on B with the magnitude F(AB).

I think I am misunderstanding the concept and how are forces transmitted through the bodies and how does Newton’s third law apply here.

I need some help here.

Thanks in advance.
 
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AmrD said:
I1. Body A is pushing against Body B with a force F(AB), Now body B will push against body A with a reaction force F(BA) equal but opposite to F(AB). Now shouldn’t be another reaction force F2(AB) due to the action of the reaction force F(BA) and another reaction force F2(BA) as a reaction to that reaction !
There are just two bodies and thus two forces involved: F(AB) and F(BA). Those forces are equal and opposite. (Using your notation, F2(BA) is the same force F(BA).)

2. Three bodies A, B and C setting on a frictionless surface in the order A, B and C. A is pushing on B with F(AB)
First, is it true that B will also push on C with the same force F(AB) and if that is true shouldn’t C also exert a reaction force on B with the magnitude F(AB).
No, it is not true. At least it's not necessarily true. If those blocks are held in place so they have no acceleration, then the force that A exerts on B must equal the force that C exerts on B. Nonetheless, they are not 'action-reaction' pairs.

I think I am misunderstanding the concept and how are forces transmitted through the bodies and how does Newton’s third law apply here.
Using your three bodies (let's assume blocks on a frictionless surface) as an example. The Newton 3rd law pairs are:
(1) A pushes on B and B pushes on A
(2) B pushes on C and C pushes on B

The force between A and B does not necessarily equal the force between B and C. To fully analyze the forces exerted, you'll need Newton's 2nd law as well as the 3rd.
 

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