Final answer:
When the third rail fails, a train loses its power supply, leading to a loss in propulsion and causing the train to stop. Atmospheric pressure differences can also create a suction force, which is dangerous for individuals standing close to moving trains.
Step-by-step explanation:
When the third rail fails, one effect on a train is that the power supply to the electric locomotive is lost. This disruption of power causes the train to lose propulsion which results in the train coming to a halt. The third rail is a critical component of the electrical system that provides power to trains, especially in light rail and subway systems. Without it, trains cannot operate, similar to how a circuit is incomplete without a power source, rendering electrical devices inoperative.
Regarding the dangers of standing close to railroad tracks, atmospheric pressure differences created when a train moves rapidly past can generate a suction force. This force can potentially pull a person standing too close to the tracks towards the moving train. The rapid displacement of air by a fast-moving train creates a low-pressure area, and since nature tends to balance differences, higher pressure from the surroundings pushes towards the low-pressure zone, potentially affecting nearby objects or persons.