An old trick to find out if a train is coming is to put your ear on the rails of the track. Why is this more effective than just listening for the sounds the train makes in air?
Soundwaves in the air will have spread out over a larger and larger area the farther they travel. Sound waves that travel through rails travel in one dimension, they don't spread out.
The the reaosn why sound waves in the rails wll stay in the rails, is because the velocity of sound in rails is much higher than the velocity of sound in the ground and in the air. This causes most of the sound waves to reflect off the boundary between the rails and the ground or air and stay in the rails.
This old trick of putting your ear on the rails of a track to find out if a train is coming is more effective than simply listening for the sounds the train makes in the air due to a phenomenon called sound conduction.
When a train approaches, it produces vibrations that travel through the rails, similar to how the sound waves travel through the air. However, in the case of rail tracks, the vibrations are conducted and transmitted more efficiently through the solid metal rails compared to the air, which is a gas.
When you place your ear on the rails, you create direct contact between your ear and the source of the vibrations. This allows the sound waves, which are essentially vibrations, to travel directly into your ear through the bones and tissues of your head. By eliminating the barrier of the air, you can pick up the vibrations more clearly and perceive the approaching train better than by simply relying on sounds in the air.
It is important to note that this trick should only be attempted with caution, as trains can be dangerous and precautions should always be taken to ensure personal safety.