# Are they Central force?

## The Attempt at a Solution

Please check if I am correct:

The following are Central force:

a.Action and reaction forces between two bodies
b.Van der Waal's force between two molecules

c.dipolar force between two small magnets
d.Force between two current carrying conductors
e.Lorentz force on a charged particle

(c,d,e) are central as long as B field is time indipendent

the following are not:

a.Viscous force on a body falling through a liquid
b.Coriolis force on a body

I do not know QM...Can you please say whether force between two electron spin will be central...

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a) It is correct only when the strong form (central,like gravity) of 3rd law is assumed.
c)It means you have taken two bar magnets and their interaction.It is not central...can be understood from its expression:
U=(const)(1/r^5)[m1.m2-3(m1.r)(m2.r)]

So,the force is NOT central.

d)Any force to be central,the force centre is to be point-like...Here it is not obeyed.
e)In electrodynamics,3rd law of motion is NOT applicable...so, central interaction betweeen two charged particles is forbidden.In magnetostatics,the 3rd law is valid...but only its weak form(npon-central form).

Force between two electron spin is like the interaction between two dipoles...so,it is also non-central force.