Why do trains take a mile to stop, even though every car has brakes on it?

273 views

I’ve been wondering about this question for a long time. Every single car in a train has its own brakes, so the train should stop in the same distance that it takes one car to stop. Why is this not the case? Or does each car take a mile to stop on its own?

In: 0

16 Answers

Anonymous 0 Comments

The heavier something is, the greater the force that is necessary to change its speed. Trains are enormously heavy and so require enormous friction to change their speed even a little. A train slows down at a rate determined by the force of friction created by the brakes. The more friction, the faster the train slows. Since each car can contribute to this friction, the force is greater than when the brakes are applied in only one car. If one car locks its brakes, as has been pointed out, the wheels will slip because the friction is insufficient to stop the whole train. But when all the cars contribute, far more friction is achieved since the friction of all the wheels must be overcome before the entire train slips. In addition, the greatest friction is achieved between two surfaces just before one breaks free of the other. So the train will stop faster if the wheels don’t slip at all, just like a car stops faster if it doesn’t skid. Even then it will take a mile because of the immense weight of the train.

Anonymous 0 Comments

The heavier something is, the greater the force that is necessary to change its speed. Trains are enormously heavy and so require enormous friction to change their speed even a little. A train slows down at a rate determined by the force of friction created by the brakes. The more friction, the faster the train slows. Since each car can contribute to this friction, the force is greater than when the brakes are applied in only one car. If one car locks its brakes, as has been pointed out, the wheels will slip because the friction is insufficient to stop the whole train. But when all the cars contribute, far more friction is achieved since the friction of all the wheels must be overcome before the entire train slips. In addition, the greatest friction is achieved between two surfaces just before one breaks free of the other. So the train will stop faster if the wheels don’t slip at all, just like a car stops faster if it doesn’t skid. Even then it will take a mile because of the immense weight of the train.

Anonymous 0 Comments

This is hilarious that everyone assumes you are talking about actual cars rather than train carriages

Anonymous 0 Comments

This is hilarious that everyone assumes you are talking about actual cars rather than train carriages

Anonymous 0 Comments

They are very heavy and their wheels are steel on a steel track. This means they have very low rolling resistance, which is part of why trains are so efficient at moving freight. Once you get it moving it doesn’t take much to keep it moving. There is very little grip between the wheel and track to slow The train down. The downside is that emergency braking takes a long time. Emergency braking also destroys the wheels and damages the track. It can take up to a mile for the train as a whole to come to a stop, they can also be over a mile long and loaded with heavy things like gravel and paper.

Anonymous 0 Comments

They are very heavy and their wheels are steel on a steel track. This means they have very low rolling resistance, which is part of why trains are so efficient at moving freight. Once you get it moving it doesn’t take much to keep it moving. There is very little grip between the wheel and track to slow The train down. The downside is that emergency braking takes a long time. Emergency braking also destroys the wheels and damages the track. It can take up to a mile for the train as a whole to come to a stop, they can also be over a mile long and loaded with heavy things like gravel and paper.

Anonymous 0 Comments

It’s the same thing as trains accelerating up to speed, there’s a lot of weight that has to come to a stop.

While yes there is a lot of contact area spread out between all the steel wheels, it’s still not enough to make stopping all that weight, with all that momentum any kind of quickly or efficiently.

IIRC passenger trains (think Amtrak or subways in the USA) have extra braking mechanisms built into the rails at each station to help bring them to a stop (please correct me if I’m wrong)

Freight trains, the big several miles long ones, only have the car brakes and again there is an immense amount of mass and momentum that has to be slowed and stopped. So if they try to stop quickly, all that’s going to happen is the wheels will slide across the rails.

Anonymous 0 Comments

It’s the same thing as trains accelerating up to speed, there’s a lot of weight that has to come to a stop.

While yes there is a lot of contact area spread out between all the steel wheels, it’s still not enough to make stopping all that weight, with all that momentum any kind of quickly or efficiently.

IIRC passenger trains (think Amtrak or subways in the USA) have extra braking mechanisms built into the rails at each station to help bring them to a stop (please correct me if I’m wrong)

Freight trains, the big several miles long ones, only have the car brakes and again there is an immense amount of mass and momentum that has to be slowed and stopped. So if they try to stop quickly, all that’s going to happen is the wheels will slide across the rails.

Anonymous 0 Comments

Usually, train brakes aren’t powerful enough to slow down the train as quickly as a car. On top of that, air brakes have a few seconds delay as the braking signal has to propagate from car to car. This is acceptable because there are more effective safety measures that can prevent the need for a train to brake quickly.

However, modern lightweight passenger trains can usually brake a lot quicker, in some cases nearly as fast as a car on regular tires. (If the track isn’t dirty)

Anonymous 0 Comments

Usually, train brakes aren’t powerful enough to slow down the train as quickly as a car. On top of that, air brakes have a few seconds delay as the braking signal has to propagate from car to car. This is acceptable because there are more effective safety measures that can prevent the need for a train to brake quickly.

However, modern lightweight passenger trains can usually brake a lot quicker, in some cases nearly as fast as a car on regular tires. (If the track isn’t dirty)