How does one locomotive have enough power to pull a train?

Question

I've seen trains that seem to go on and on forever, especially when I'm waiting for it to pass! It seems impossible that one locomotive could harness enough energy to do this. Is there something I'm missing or are locomotives really that powerful?

Answer 1

Here the key dude- The locomotive gets TRACTION aka tactive effort, and the cars have steel wheels on a stell rail so there is little friction and resistance to the pulling force. I imagine a long string thru the train ( the drawbars) and a locomotive pulling the string...wha la, a train moves.  That' partly why locos are so heavy and carry sand ....to get traction on the steel rail

Answer 2

when the time goes on the diesel locomotive they are creating more powerfull locomotives.  so it is possible for one locomotive to pull a lot of stuff.  also depends on where u are at and what there carring.

Answer 3

It's very seldom we have a train with only one engine pulling it(at least not for a mainline freight train).That being said our newer locomotives are mostly 4000 and 4400 horsepower.All that power drives a generator to supply electricity to traction motors to turn the wheels.They can pull an incredible amount of weight.We have empty coal trains that are 120 cars or more,but since they are made from aluminum the train only weighs about 2500 tons.We run those using two engines.One engine would pull it but not very fast if you had any kind of grade to climb.

Answer 4

You're not missing anything.  Locomotives are extremely powerful and built to pull.  But, they get some help from the immutable laws of the physical universe.

A locomotive doesn't start the whole train moving at once, usually.  It starts the first car, then the engine and that car start the second, then the engine and those two cars start the third moving, and so on.  This is do-able because there is "slack" between each car in the train, via the "draft gear."  

A body at rest tends to stay at rest.

A body in motion tends to stay in motion unless acted upon by an external force:   inertia and kinetic energy.

So, just as taking up the links in a chain, one by one, the train starts moving, then it wants to keep moving.

Sometimes, if the slack in the train is stretched too tight, the locomotive can't start the train moving.  So, the engineer uses a method called "taking slack."  The engineer reverses then engine, and moves backwards some sufficient distance, depending on conditions.  This creates the necessary slack.

When moving forward now, the engine starts the first car, which starts the next, etc.  This was a very frequent occurance when steam engines plied the rails because, although very powerful as well, steam engines didn't have the "starting tractive effort" available with the use of electric motors.

But the practice is not extinct.  On some yard jobs, locals and work trains, you take what they give you, and you only have one unit to work with, often times.  And, when out on the road, engine failure happens, and you wind up with one unit working, sometimes.  So, when needing to take slack, you do.

In a paradox, it can be accurately stated that, a diesel electric will start more tonnage than it can pull and a steam engine will pull more tonnage than it can start.  If the two technologies were combined, it would be the ultimate hybrid pulling machine.

Sometimes, to increase adhesion of the locomotive drivers, sand is applied to the rail to increse the friction, thereby increasing the traction available.

But, if you do get the tonnage moving, the real trick is getting the thing stopped where you want it to, again thanks to inertia.  One propulsion system, four braking systems:  Automatic air brakes (on the cars), engine or "independent" brake, dynamic brake and the hand brakes.

Answer 5

It takes a lot of torque plus once you get them moving it's not that difficult. It's like if you started to push a car. It's hard to get it rolling, but once it does start rolling you can almost start to jog along side it.

Answer 6

Diesel electric locomotives of almost 5,000 horsepower are common today, and they can be grouped together to produce multiples of that power.

So there is no secret to it.  It is a matter of sheer power.

Answer 7

All good answers and the subject is quite adequately covered.

I will add one little thing to think about, it is quite possible to pull a train on average gradients with less than one horsepower per ton.

Think about that for a second: it would be like putting a 3 hp lawnmower engine in a pickup and hooking onto a trailer and trying to pull it.

Steel wheels on steel rails have almost NO friction.

Answer 8

It's not only a question of power but traction force to get a train in motion. The electric locomotives I am driving can develop a traction force of 300 to 480 kN in one unit! The power of up to 8,000 hp and briefly more makes it able to accelerate heavy freight trains in no time and hauling these at an average speed of 55 mph to 90 mph (90 - 140 kmph). And it needs a lot of power to haul a fast container freight train at 140 kmph up and downhill via our mountainous high speed lines in Germany.

Answer 9

All of the other posters have it right about diesel locomotives being mean pulling machines.

Here are some numbers:

A typical modern diesel locomotive weighs 405 tons.

With the latest computer control systems (and dry rail), they can develop about 180,000 lbf of "pull".

Put three of them together, and you have more than 1/2 million pounds of pulling power!!

On flat terrain, that'll get more than 100 cars moving very well.

Be careful, or you'll break a coupler !!