Does This System Of Electric Charges Violate Conservation Of Energy? Imagine a system of 3 point charges and some kind of circular "rail".
All charges have the same magnitude - 2 are positive and one negative.
One positive charge is placed at some distance from the center of the circular rail.
The two other, are "glued" together so they must move together, and they are placed on the rail which 
force them to move only on the rail path.
Now imagine i give them a slight push.
Calling the glued charges the "system", We can say that the force between the system and the positive charge outside the rail is both attractive and repulsive (depending on what part of the rail the system is) but we can identify that the Parallel component of the force (with respect to the velocity vector) will always be in the direction of motion.
Thinking it through, i think you will agree that the charges on the rail will accelerate every 1 period - 
therefore "generating" energy !
Can you spot what's "wrong" here ? 

In this figure i used rectangular charges just to make it more clear, The "Paradox" is of course about point charges.
 A: In the bottom position, if there is some space between the two charges the positive charge at the bottom will push the positive charge away and attract the negative charge. This tends to push the two charges clockwise. 
At the top the negative charge will be pulled towards fixed positive charge, while the positive charge will be repelled, so the force is anticlockwise. The force at the sides is weak because there is a force on both charges, but one there will be a greater force on the charge closer to the fixed charge. Again the force is anticlockwise. 
So the moving charges will be speeding up at the top and sides, but decelerating at the bottom. I expect that they would all balance out over a full cycle.
A: You are imagining that the little blocks behave like positive charges when looked at one way, but then when they turn around, they become negative charges.
Actually, they would behave like dipoles. At any position on the ring, the positive end will have a repulsion force and the negative end will have an attractive force. In the general case, the two forces will be slightly different in magnitude and direction (because of the physical size of the dipole, the two ends have different displacement vectors from the source charge).
If you plot the resultant vector as a function of angular position around the ring, you will find that it can point in any direction; sometimes it has a clock-wise component and sometimes anti-clockwise. For example, at the 6 o'clock and 12 o'clock position, the resultant is tangential and clock-wise (so going against the assumed motion). In the region of 1, 5 and 7 and 11 o'clock, the resultant is radial so not affecting the rotation. At other times the vector is in various directions. Symmetry alone is enough to tell you that there will be no net force after one orbit.
The effect of all of this is that the dipoles have a rollercoaster ride around the ring - sometimes they are accelerated, sometimes decelerated, sometimes coasting. There will be stable and unstable equilibrium positions.
So if launched, your rig would orbit in a raggedy manner until friction stopped it.
