This discussion clarifies the forces experienced by two positive charges, q1 and q2, when one charge is held still. It establishes that q2 does not experience a force due to itself and that the forces acting on q1 and q2 are equal in magnitude but opposite in direction, as per Newton's Third Law. The net force on each charge is not zero when considered individually, but the forces do not "cancel" each other out as they act on different objects. The correct expression for the force between the charges is given by Coulomb's Law, specifically ##F = \frac{k*q1*q2}{r^2}##.
PREREQUISITESStudents of physics, educators explaining electrostatics, and anyone interested in understanding the principles of force interactions between charged particles.
Since q2 cannot push q1 away, that force does not push q2 away?Mister T said:q2 does not experience a force due to q2.
Whether or not q1 is held in place, the repulsive force exerted on each charged particle is still there. BTW, there's no factor of 2 in the expression for the force.
annamal said:Since q2 cannot push q1 away, that force does not push q2 away?
No, it wouldn't. When q1 is held in place, the net force on q1 is zero. Release q1 and the net force on q1 is ##\frac{kq_1q_2}{r^2}##. The net force on q2 has the same magnitude. The forces act on different objects, so you don't add them together.annamal said:If q1 were let go, the total force would include the factor of 2?
Ok, so the net force of the q1 and q2 charge would be 0 since they exert equal and opposite forces even though there is a net force on q1 and q2 individually?Mister T said:q2 cannot exert a force on itself. It has nothing to do with q1 being held in place.No, it wouldn't. When q1 is held in place, the net force on q1 is zero. Release q1 and the net force on q1 is ##\frac{kq_1q_2}{r^2}##. The net force on q2 has the same magnitude. The forces act on different objects, so you don't add them together.
It's just like me pushing on a block with a force of 10 N. The block pushes on me with a force of 10 N. I don't add them to get 20 N because the forces are acting on different objects.
If they're both free to move then the center of mass does not move - so yes.annamal said:Ok, so the net force of the q1 and q2 charge would be 0 since they exert equal and opposite forces even though there is a net force on q1 and q2 individually?
The net force on q1 is not zero. The net force on q2 is not zero. They exert equal but opposite forces on each other (Newton's Third Law).annamal said:Ok, so the net force of the q1 and q2 charge would be 0 since they exert equal and opposite forces
I mean it is 0 in a system with both q1 and q2 since they cancel.Mister T said:The net force on q1 is not zero. The net force on q2 is not zero. They exert equal but opposite forces on each other (Newton's Third Law).
They do not "cancel". In this context "cancel" means "adds up to zero". But these forces act on different objects. Even if you consider the system consisting of q1 and q2 then the forces are internal. Newton's Third Law requires that forces occur in equal-but-opposite pairs. To say this pair "cancels" is a misconception.annamal said:I mean it is 0 in a system with both q1 and q2 since they cancel.