Comment by litenboll | Hacker News Reader

Comment by litenboll | Hacker News Reader

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I had a summer job once, filling trains with sugar. They weighed about 15kkg per wagon (usually 5-10 wagons per train IIRC).

One time the pulling cart broke down and we had to switch it for another, but when we took it off the rails we forgot about the "shoe" that is supposed to go between the rail and one of the wheels so it can't move downhill (it was like 1degree of slope so barely recognizable as a slope).

It started moving extremely slowly, and all of us except one tried to hold back the force of the train, which of course was imossible and dangerous. The one who did not try to push it very quickly found the "shoe" and put in place. Initially it did not seem to help at all, the train just continued moving at the same pace, tearing up asphalt with the shoe. It finally came to a stop after about 3-5m(?) which takes a fair bit of time with such low speed, and felt like forever given the situation.

The train tracks headed out into an open road, so it could have been so much worse if it were not for the only person thinking clearly in the situation (he was one of the more experienced in our group).

Also want to highlight this for another reason. At slow speeds rail and boats suffer from far less “moving” friction than road vehicles. So once off there is very little slowing them down vs cars and trucks that suffer from high rolling friction.

Grady Hillhouse of Practical Engineering recently did a great demo of this. He was able to pull his car in neutral and an empty train car on rails with roughly the same force.

https://www.youtube.com/watch?v=nGhBHrr5CYQ

One wonders how braking works on a train.

Mostly the same as it would work on a car with a brake shoe applied to the steel wheel.

The only major difference is that they often use a safety air brake system shared across an entire consist (train) that requires “charged” pressure (above atmosphere) to disengage the brake (although I think they have moved to an electronic system that now monitors air pressure in each car individually).

Semi trucks have air brakes that function very similarly. One air source for all brakes, pressure releases, brakes lock on failure.

I think it's actually in an earlier video, and he wasn't able to actually pull the train car due to track irregularity -- but according to calculations he should have been able to if there was a safe way to give it a bit of a nudge.

You're absolutely right; I posted the wrong link.

https://www.youtube.com/watch?v=tfA0ftgWI7U

A friend of mine was on the light rail here downtown when it stopped unexpectedly. He was confused and walked outside only to see the train had hit a fire truck and pushed it nearly a block before it stopped. He had no idea there was even a collision inside the train.

Trains are very scary stuff even when moving at a crawl.

A 110,000 ton ship collision is something the human brain is just not going to understand intuitively.

> all of us except one tried to hold back the force of the train

This reminds me of a vivid memory I have. I’d just finished a shift cooking, and out back of our restaurant there were railroad tracks. I had a beer and smoke out there with my shift mate, and a train was rolling by. I thought it would be fun to practice jumping on the train. So I do a few passes jogging alongside it, hopping on and off. Then my buddy, standing still, reached out and grabs a rung of a ladder on one of the cars. It immediately picked him up, but he gripped harder due to being startled. He got ragdolled through the air about 10 feet from where he was initially standing.

Kids, don’t play with trains (trespassing issues aside).

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