Final answer:
Train operators should be vigilant against sliding wheels on yard tracks under conditions that reduce friction, such as adverse weather or track contaminants.
Step-by-step explanation:
A train operator should be particularly alert to guard against sliding wheels on a yard track when conditions such as weather (rain, snow), track contaminants (oil, leaves), or improper braking techniques create a scenario where the coefficient of friction between the train wheels and the track is reduced. When the wheels slide, it can cause flat spots on the wheels, making them uneven and can lead to derailment or damage to the track structure.
In a similar manner, passengers should maintain a safe distance from rapidly moving trains due the effect of atmospheric pressure. A rapidly moving train can create a low-pressure area that can draw objects, or even people, towards it, posing a significant risk.
Understanding these dynamics is crucial for ensuring safety in the railroad system. It's important for train operators to monitor for changes in conditions and to adjust their operations accordingly to maintain safety.