- #1
sokrates
- 483
- 2
Greetings the venerable PF society,
I have a question that has been lingering in my mind for a while, so I thought I'd ask it here.
Firstly, how far below does the action-reaction (Newton's third law) principle go down fundamentally? How far below can I take it with me so that I don't make gross mistakes? Or else does it not break down at all?
Please enlighten me on the meaning as well: "To every action there is an equal and opposite reaction." (from Wikipedia)
What does this mean? Why would you necessarily have an equal an opposite force for every acting force element?I know from informal discussions that it breaks down for some specific cases, but I don't know how severely that's the issue.
I just need to connect it up to something I know better, so any help or general remark would be useful.
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BTW, the context I am going to use it is the effect of spin polarized electrons flowing through a magnetic body, namely spin-torque. It happens that the magnetic body itself feels a torque because it exerts a torque on the incoming spin-polarized electrons to align their spins. So essentially it's an action-reaction type of interaction. But I don't know if that's truly the most fundamental picture
Thanks!
I have a question that has been lingering in my mind for a while, so I thought I'd ask it here.
Firstly, how far below does the action-reaction (Newton's third law) principle go down fundamentally? How far below can I take it with me so that I don't make gross mistakes? Or else does it not break down at all?
Please enlighten me on the meaning as well: "To every action there is an equal and opposite reaction." (from Wikipedia)
What does this mean? Why would you necessarily have an equal an opposite force for every acting force element?I know from informal discussions that it breaks down for some specific cases, but I don't know how severely that's the issue.
I just need to connect it up to something I know better, so any help or general remark would be useful.
----------
BTW, the context I am going to use it is the effect of spin polarized electrons flowing through a magnetic body, namely spin-torque. It happens that the magnetic body itself feels a torque because it exerts a torque on the incoming spin-polarized electrons to align their spins. So essentially it's an action-reaction type of interaction. But I don't know if that's truly the most fundamental picture
Thanks!