Foundations: Newton's Third Law and time reversal invariance

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SUMMARY

This discussion centers on the principles of classical dynamics, particularly Newton's Third Law and its relationship with time reversal invariance. Participants argue that Newton's original formulation is outdated and that the Third Law should not be treated as an independent principle but rather as a consequence of conservation of momentum. The conversation highlights the importance of time reversal invariance and Noether's theorem in understanding symmetries and conserved quantities in physics. The consensus suggests that a focus on conservation laws may be more beneficial for novice learners than strict adherence to the Third Law.

PREREQUISITES
  • Understanding of classical mechanics principles, including Newton's laws.
  • Familiarity with vector notation and its application in physics.
  • Basic knowledge of conservation laws, particularly conservation of momentum.
  • Introduction to Noether's theorem and its implications in physics.
NEXT STEPS
  • Study the implications of Noether's theorem in classical mechanics.
  • Learn about Lagrangian mechanics and its role in modern physics education.
  • Research the concept of time translation invariance and its relationship to energy conservation.
  • Explore advanced topics in classical dynamics, focusing on conservation laws and their applications.
USEFUL FOR

Physics educators, students of classical mechanics, and anyone interested in the foundational principles of dynamics and their modern interpretations.

  • #31


Shahin.Omar said:
When you start saying things like; 'good definition of exist or real', 'fictitious forces', 'pseudo forces', 'complicated nature of the issue', 'true vs apparent', 'ifs and buts'. Sorry to say, but they only mean one thing, you have failed to grasp it!

Imagine you are a judge, and there is a witness who uses phrases like the above, what impression would you get?

When you say 'it is complicated' what you really mean is 'it is complicated for me'. When it is complicated for you, tell me what would it be like for the kids, and this is the point here?

On the surface of Earth or inside an accelerated spaceship, you feel the same thing; your weight or gravitational mass' where is the complicacy? You start using terms like d'Alembert's force and it is bound to look complicated.
OK, since you have grasped the issue and it is so simple and you are so smart and I must be an idiot to have ever thought it was complicated please post your clear and easy definition of "exist" which can be applied to forces to show that the forces you listed do exist and inertial forces do not.
 
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  • #32
I think this thread has been thoroughly hijacked and gone off the deep end. If the OP has further questions, please contact me to reopen this thread.

Zz.
 

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