Final answer:
The danger of standing close to railroad tracks when a commuter train passes is due to atmospheric pressure and aerodynamics, as the fast-moving train creates a pressure gradient that can pull a person towards it.
Step-by-step explanation:
The question posed concerns the physical phenomena that can make standing close to railroad tracks dangerous when a fast-moving commuter train passes by. This scenario involves the principles of atmospheric pressure and aerodynamics, crucial in understanding the forces at play.
When a train moves rapidly through the air, it pushes air out of its way, creating a high-pressure wave at its front and low-pressure areas in the surrounding space. This effect is similar to the way an airplane's wing generates lift by creating different pressure regions above and below the wing. The high-pressure air ahead of the train and the low-pressure air behind it can create a pressure gradient.
As the train passes by, the low-pressure area following it effectively sucks air toward the train. Due to the rapid displacement of air, someone standing near the tracks can feel a strong pull toward the train. This is a result of the atmospheric pressure being greater on the side of the body furthest from the train, pushing the person towards the train where the pressure is lower. This dynamic is a direct demonstration of Bernoulli's principle, which states that an increase in the speed of the fluid occurs simultaneously with a decrease in pressure. Here, the 'fluid' is the air displaced by the train.