How exactly do you find the net force between charges?

[paki123]

I was doing some homework problems, and I came across a couple I didn't know. I then realized I must have screwed up my understanding on electrical forces.


For an electrical force, if there are two protons, the force is k*q1*q2/r^2. The direction is in the opposite direction.

<---(+) (+)--->


Right?

What would be the net force there assuming the charge is e? Would it be 0 since they are in the opposite direction and have equal distances?

My question is it possible to have a third electron and still have the net force equal to 0?

 

[Philip Wood]

Yes and Yes! If \textbf{F}_{i, j} means the force that charged particle j exerts on charged particle i, then \textbf{F}_{i, j} = \textbf{F}_{j, i}. In other words the forces between the particles are equal and opposite.

For three particles,
the force on particle 1 is \textbf{F}_{1, 2} + \textbf{F}_{1, 3}
the force on particle 2 is \textbf{F}_{2, 3} + \textbf{F}_{2, 1}
the force on particle 3 is \textbf{F}_{3, 1} + \textbf{F}_{3, 2}

So the net force, that is the forces on all three particles added together, is zero, because
\textbf{F}_{1, 2} = -\textbf{F}_{2, 1} and so on.