# Doubts about the strong and weak versions of Newton’s third law

I was going through some assertion and reason questions.

(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
(e) Both A and R are false.

Statement A:

For a system of two charges $$q_1$$ and $$q_1$$ at a separation $$r$$, the Coulomb force of $$q_1$$ on $$q_2$$ and that of $$q_2$$ on $$q_1$$ are equal and opposite, and these may or may not act along the line that joins $$q_1$$ and $$q_2$$.

Statement B:

According to Newton's third law, action and reaction forces are equal and opposite but these may or may not act along the line joining the two particles

My doubts:

According to the strong version Newton's third law, the forces must act along the line joining the two particles. So by “Newton's third law,” do we mean the weak version of Newton's third law? If so, why? If someone could provide a translated version of Newton's paper it would be helpful.

Does the Coulomb force follow the strong Newton's third law or the weak Newton's third law?

Does the Coulomb force ignore the fact that Newtonian mechanics cannot be used for small particles like electrons and protons, and rather we have to use quantum mechanics? (I don't know much about quantum mechanics.)

And lastly, what is the answer?

So by “Newton's third law,” do we mean the weak version of Newton's third law?

Yes.

If so, why?

Why is Newton's third law known as *weak law of action and reaction*?

Does the Coulomb force ignore the fact that Newtonian mechanics cannot be used for small particles like electrons and protons, and rather we have to use quantum mechanics.?

What is the range of the validity of Coulomb's law?

Does the Coulomb force follow the strong Newton's third law or the weak Newton's third law?

Electrostatic forces obey the strong form of Newton's third law. Hence statement A is false.

Statement R is true, since by “Newton's third law,” we mean the weak form of Newton's third law.