Final answer:
The force between the hot and neutral lines hung from power poles is repulsive due to opposite directions of current flow, causing a magnetic repulsion between them. However, due to the alternating nature of the current, this effect averages out. For three parallel wires with outer currents in opposite directions, the middle wire will be repelled by both.
Step-by-step explanation:
The force between the hot and neutral lines hung from power poles can be determined by understanding the principles of electromagnetism. Specifically, two parallel conductors carrying current will exert magnetic forces on each other. If the currents are flowing in the same direction, the wires will experience an attractive force; if the currents are in opposite directions, they will experience a repulsive force.
Given that in a typical alternating current (AC) power system the current in the hot and neutral lines flows in opposite directions, we can conclude the force would be repulsive. However, because the current direction alternates, the net long-term effect averages out, and the lines do not push away from each other in a noticeable manner.
In the case of three parallel wires with the outer two having opposite current directions, the middle wire will experience repulsion from both the outer wires. This is because the magnetic fields created by currents in opposing directions result in forces that push the wires apart.