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This time’s question is a friend’s inquiry. He recently came across a railroad crossing. For those of us who have spent time in smaller towns in this country, railroads through the middle of the road are rather common. Now he was under the impression that the steel rails have some kind of grooves into which the wheels of the train fit. But when he saw one of these rail crossings recently, he noticed that the road and the rails were at the exact same level, with no space between them- there is no space for the train wheels to fit around the rails- no groove mechanism.

HugoSnapNow as someone who has seen a lot of drama films, the fairly common scene of a fast moving train breaking hard and sparkles flying besides the wheels, is quite strongly etched in my memory (like this one from Hugo)- The groove idea never crossed my mind. I always thought that the wheels moved on the rails. But my friend’s question made me think- why don’t trains slip from the rails? This might sound silly to some. But it really isn’t obvious to me. Of course, friction is at play here. But that isn’t a satisfactory hint at all. Trains with the speed they move at, ought to slip on something as smooth as steel rails. But they don’t. Why?
If you know the answer, and it is very obvious to you, please don’t use it as an excuse to not answer. Enlighten the rest of us.

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6 Responses

  1. I love trains and I also love trains. Its the ingenious track design that comes to the rescue. They might seem to be a fairly basic thing to look at but there were lots of trials and errors and simple physics that went into the development of the perfect track esp. for high speed trains. The Japanese guys also have to keep in mind the strong earthquakes while designing them which is a big challenge. In this documentary, which is one of my favourite, Richard Hammond explains many things about them. The track part comes after 4:00. Thanks for posting this and making me watch it all over again!

  2. Great. Post the documentary please :-)

  3. Ah sorry forgot to attach the link http://bit.ly/trainsDocumentary

  4. Bullet trains might have different mechanisms for banking and travelling at high speeds. But for trains elsewhere travelling at around 100 km/h its the weight of the train that keeps it from slipping. I remember understanding in class 12th the concept of friction and slipping when the force that causes the movement overpowers the friction. Interestingly enough if tracks had a groove mechanism or any other equivalent of grooves to increase friction, trains in their present weights will have hard time moving. I conducted this experiment in class 8th where I was making a suspension railway and I made the track using paper mache technique but since the paper mache construction was rough train moved with little speed then I added rubber grip onto the metallic rollers(equivalent of wheels of ground train) of the train, for the better grip but that made it worse. Then I made the tracks out of Aluminium sheet and since the rollers were already of aluminium I could get my train rolling at good speeds. To find an explanation for this effect I talked to Sanjeev Mittal (now DRM for Hubli division of South Western Railway) and he told me that the friction has to be so less for the train to move forward.

  5. Like Miss/Mr/Mrs S, i also love trains. Its easier for the train to run on the steel rails rather than on any other medium. And i think the grooves are made at the railway crossings to avoid train from slipping onto the road which is at the same level. The protruding part of the wheel moves into the groove at the crossings or other same level surfaces and train runs on the rails like any other vehicle on the road at all other places including the point where two tracks converge or diverge.

  6. […] (This post is in response to Wednesday’s Post, Railroads) […]

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