Curious George

A fountain of material and immaterial information - Things that I spend my days wondering about... and perhaps you have been too? Check out for more curious questions (and answers to them)

Monday, March 24, 2008

Ears popping in train tunnels

A friend of mine recently went to Japan and the took the bullet train. Going several hundred km/hr he experienced a fairly considerable popping in the ears (or propper i ørene as we like to say in Norway).
Now why does this happen?
Curious George took the dive and the easiest way to think of it is imagining that the tunnel is filled with water. When the train enters the tunnel, the water has no-where to go, and is pressed in front of the train, while some escapes "backwards" - this creates a suction in the train, just like what happens when you open your windows going 90 mph - your ear pops and maps and papers go straight out the window.
So when a train hits a tunnel, the accelerated air-flow around the train creates a vacum causing your airs to pop. Just like it would when you are on an ascending airplane.
An air-tight train would solve it, but this is costly and dificult to make. You can also design the tunnel to reduce this effect - ex through air-vents (though if the airvents are too big and too far apart it would feel like you go in and out of a tunnel all the time) or just a bigger tunnel, so that there is less pressure-buildup infront of the train.
The english channel tunnel is an excellent solution to this. Being 30 miles and under water, the "Chunnel" is actually two seperate tunnels connected by cross passages. This greatly improves the air pressure problem.
George says Hona sainara and good luck on ear train popping


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