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Saturday, Aug 17, 2019

Mumbaiwale: What happens when scientists take a Mumbai train?

They look at the physics of cables, sound of the moving coaches and the magic of a rail ride. Learn more about them at a Sunday session

mumbai Updated: Jul 20, 2019 07:40 IST
Rachel Lopez
Rachel Lopez
Hindustan Times
Mumbai locals have something unique: Their Auxiliary Warning System, a network of sensors and magnets on the tracks and in the trains, automatically apply brakes and stop trains even if one somehow passes a red signal.
Mumbai locals have something unique: Their Auxiliary Warning System, a network of sensors and magnets on the tracks and in the trains, automatically apply brakes and stop trains even if one somehow passes a red signal.(HT File)
         

Take a train tomorrow. To Matunga. Think of it as prep. Because even if you’ve been taking trains all your life, Sunday morning’s session of Chai & Why will probably be a revelation. The Tata Institute of Fundamental Research’s long-running science-outreach series has tackled everything from fireworks to magnets. This time, they’re taking the train.

Arnab Bhattacharya has loved trains since Class 8, when he started commuting to school in Colaba from his family’s new home to Mulund. “I took the 7.13 in the morning and the 4.40 back,” he recalls. “They fascinated me – why did the compartment after the Ladies make a DRRRRR sound? How could passengers read the train signals and know which side the platform would be on? If there’s one thing that connects Mumbai, it’s the trains.”

His colleague Mahesh Gokhale, a scientific officer, spends close to four hours a day on his commute, so it’s safe to say he’ll have more than textbook knowledge. See what keeps their minds on track:

Mumbai locals have something unique

Their Auxiliary Warning System, a network of sensors and magnets on the tracks and in the trains, automatically apply brakes and stop trains even if one somehow passes a red signal.

Your ears might pop between Thane and Kalyan

Those who take a fast train to Kalyan will know the funny sensation when the train whooshes through the Parsik Tunnel after Thane. “It’s basically the same reason our ears pop sometimes in an aircraft or skyscraper elevator,” Bhattacharya says. “There’s a change in air pressure. On ground, a train can just push the air in front of it to the sides. Inside a tunnel, the train acts like a piston, the air doesn’t have anywhere to go, and this causes a change in air pressure in the compartment.”

There’s music on the tracks

The rails are embedded with tech that creates sound – humans can’t hear it but the railways’ electronic system can. The sound denotes whether a section of track is occupied by a train or is clear. The Audio Frequency Track Circuit means the tone (think of your phone keypad 10 years ago) will change a bit if the track is pressed by a train. “It’s a lot more sophisticated than that, of course,” says Bhattacharya.

The signals can sense if a bogie comes loose

Some of those boxes by the side of the signals count how many wheels go by each time a train passes. These axle counters expect 48 wheels when a 12-car rake goes by. “If the same number of wheels don’t go by the next signal, it probably means some part of the train has not crossed completely or perhaps even got disconnected, and this would then force the signals to go red or into a safe state.”

They get a wire to suspend without dangling

It’s simple tech. Any rope or wire hanging under its own weight will sag. But electric wires need to be almost at a constant height so that the pantograph on the roof of the train can be in contact with them at all times? How do they do it? “They hang another wire from the first one, in short segments. One that sags as expected, the other remains almost flat.”

Each train is also a generator

When your train slows down, it is actually converting the energy of its motion back to electricity and feeding power back to the grid. “This saves electricity worth almost Rs 50 lakh per rake per year!”

That DRRR sound in some old compartments is not for show: It is made by the coach with the pantograph, the middle coach of a three-coach unit. A compressor under the seat gets turned on periodically to replenish the compressed air in the tanks so that the pneumatic brakes and pantograph can be operated. “It is turned on periodically, but is most noticeable when the train is stopped at stations and there are fewer competing sounds,” he says. “People apparently loved the seats above the compressor. In the good old days of wooden seats, they supposedly had no bugs.”

Prepare for experiments

Chai & Why scientists will help you work out the speed of a train from the rhythmic dhadak-dhadak sound and tell you why train wheels are conical, not perfectly cylindrical. The sessions are free. Just show up at 11 am at Ruparel College on Sunday. And all sessions are webcast live on their Facebook page too.

First Published: Jul 20, 2019 00:10 IST

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