Understanding Newton's Third Law of Motion: A Law of Forces Explained

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Discussion Overview

The discussion centers on the interpretation of Newton's Third Law of Motion, particularly whether it should be viewed primarily as a law of forces rather than a law of motion. Participants explore the relationship between forces and motion, and how these concepts are articulated in Newton's laws.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant suggests that Newton's third law is fundamentally about the nature of forces, emphasizing that forces exist in pairs of equal magnitude and opposite direction.
  • Another participant argues that forces cannot be considered in isolation from the bodies they act upon, asserting that motion is inherently linked to the forces described by the third law.
  • A participant questions why the superposition of forces is not classified as a law of motion, indicating a potential overlap with Newton's first and second laws.
  • Some participants reference the concept of "net" force in Newton's first and second laws, suggesting that these laws already incorporate the principle of superposition.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of Newton's third law, with no consensus reached on whether it should be classified primarily as a law of forces or a law of motion. The relationship between forces and motion remains a point of contention.

Contextual Notes

Some participants note that the discussion involves assumptions about the definitions of forces and motion, and the implications of the term "net" force in the context of Newton's laws. These aspects remain unresolved.

Dschumanji
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It is clear that Newton's first two laws of motion deal with motion: the velocity of a moving body is persistant, and net forces cause acceleration of such a body. However, in my opinion, the third law has more to do with the nature of forces rather than motion. The main point is that forces come in pairs of equal magnitude but opposite direction.

Newton's third law of motion should be considered a law of forces, such as the superposition of forces is a law of forces.

Any thoughts on this idea? Am I just being crazy?
 
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Well a force is often associated with motion isn't it? The problem with considering it as a matter of force alone, is that it seems rather disconnected; if body A exerts force F on body B it itself experiences F in an opposite direction. You can't talk about forces alone without considering the bodies and their subsequent motion induced by the forces. Which is why a more accurate statement of Newton's third law makes references to bodies and not just forces.
 
Defennder said:
Well a force is often associated with motion isn't it? The problem with considering it as a matter of force alone, is that it seems rather disconnected; if body A exerts force F on body B it itself experiences F in an opposite direction. You can't talk about forces alone without considering the bodies and their subsequent motion induced by the forces. Which is why a more accurate statement of Newton's third law makes references to bodies and not just forces.

So why isn't the superposition of forces itself considered a law of motion?
 
I thought that was covered in Newton's 1st and 2nd law, which makes references to a "net" force.
 
Defennder said:
I thought that was covered in Newton's 1st and 2nd law, which makes references to a "net" force.
It makes use of the principle but is not covered in the first or second law.
 
It is given in the statement of the first two laws. The laws use the word "net" which is essentially the superposition principle.
 

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