Can electric dipoles violate Newton's 3rd Law?

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SUMMARY

The discussion centers on the interaction between an electric dipole and a test charge, specifically examining whether this interaction violates Newton's Third Law. It is established that while the forces on the dipole by the test charge may appear to cancel, they do not actually do so, thereby preserving momentum conservation. The conclusion drawn is that Newton's Third Law remains intact, as the forces exerted by the dipole and the test charge do not lead to a net force cancellation in the z-axis direction.

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Suppose you have an electric dipole centered at the origin and aligned with the z-axis. If you place a test charge somewhere in the x-y plane, you can show that the force on the dipole by the charge cancels to be zero, yet the dipole still seems to exert a force on the charge...

If this is true, then this is a violation of Newton's third law, and this also means that momentum isn't being conserved (at least not the sum of the momentum of the dipole and of the charge).

Is this situation valid, and is this something which can really happen? If so, where is the momentum going - the electric field somehow?
 
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dipole said:
Suppose you have an electric dipole centered at the origin and aligned with the z-axis. If you place a test charge somewhere in the x-y plane, you can show that the force on the dipole by the charge cancels to be zero, yet the dipole still seems to exert a force on the charge...
...

Why do you think forces cancel? As far as I see it, they most certainly do not! Let say dipol is oriented to +z and test charge is positive. Repulsive force z component will be negative, and attractive force by negative part of dipol will have z component also negative, so you don't have cancellation.
 
I just realized my error, Newton's 3rd law is safe!
 
Last edited:

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