Superposition and Electrostatic Force

[AirForceOne]

Suppose we have three charged particles arranged in a line, the first one being negative, the second being positive, and the third being negative.

If we want to find the net force on the third particle, we sum the force from the second particle on the third and the force from the first particle on the third.

Apparently, there is a force between the first and third particle. According to the book, this is due to the superposition principle, in which the first particle acts on the third as if the second particle is not there.

Flipping to the part about superposition, the book simply states that, by superposition, the net force on anyone of them will be the vector sum of the forces due to each of the others.

This explanation doesn't really help me understand how it is possible for there to be a force between the first and third particle. Can anyone explain how the superposition shows this? Thanks.

 

[graphene]

Do you mean to say that the presence of the second charge in between the 1st & 3rd would prevent any interaction between them ?

 

[K^2]

Superposition principle states that the electric field caused by two particles is the vector sum of the fields caused by each particle. Is that clear enough?

What generates force on a charged particle at rest is the electric field at that point. The electric field will be given by sum of the fields from first and second particles.

$$F_3 = q_3 E = q_3 (E_1 + E_2) = q_3 E_1 + q_3 E_2$$

But that's just sum of the forces caused by q₁ alone and q₂ alone.