Why Locomotives Can Pull So Much

In today's video, we go over all the things that allow locomotives to pull trains many times their weight.

[johnjohnii]

When I was a kid, my grandpa took me to a siding in town where they parked covered hoppers waiting to be loaded with silica. He uncoupled one and released the handbrake before pushing it probably 25ft, then rolled it back by hand. Seeing that at 5 years old, I thought he was like superman or something.

[davel]

I'm led to believe that some subway networks have stations at the crest of a slight incline. This means that the train is effectively using the up hill section before the station to help slow down and the downhill section immediately after the station to speed up. A pretty simple system when you think about it but it must save a lot of energy and brake wear.

[asds]

This answered so many questions! Great explanation of the draft gear. I'm from Colorado, and I always wondered how much weight a train gains in a snowstorm - I'm thinking it has to be significant.

[Greatdome]

Wheel-rail friction is minimal compared to wheel bearing friction. Wheel flange friction on curves can be significant, too.
Coupler slack also includes coupler-to-coupler (loose fit) slack, most apparent in model trains.
Locomotive traction control systems actually exceed the theoretical friction limit (mu = ~0.3) by pulsing the traction motors as do your car's anti-lock brakes.

[James_Knott]

Years ago, I worked for CN and in the mid 70s often rode on freights. One thing I soon found out is the engineer didn't want to stop the train, if he didn't have to. So, he'd bring it down dead slow, allowing me to hop on or off. If I had equipment to carry, I'd have to space it out alongside the track and hand it up, a piece at a time, to a crew member.

BTW, one detail about starting a slack trains, the more cars that are moving, the more momentum that can be used to move more cars.

[kens.]

Never realized the friction point between the train wheel and the rail is only the size of a dime. Sand and traction motors are huge for locomotives to move. Thanks! 👍

[wayneparker]

This was a very clear and concise explanation of how locomotives can move so much weight. Thank you for taking the time to explain the physics and engineering behind locomotives. 👏👏👏

[doughuffman]

I’m old. Trained in physics. I never knew before the essential function of the Draft Gear. Thank you very much. Thank’s for the sweet Southeron accent! God Bless y’all.

[doxielain]

I used to be a freight hopping traveling punk, and spent many an hour listening to cars shuffle around in the yard. I had no idea that slack was a design feature, not a bug. Thanks!

[Peasmouldia]

Rolling resistance and friction are related, but not the same. Inertia is a factor even in a zero friction situation.
Issac Newton was yer man were laws of motion are concerned..
Thanks and blessings brother.

[DEtchells]

That’s so interesting about the slack being needed for the loco to start the train - it makes total sense but never occurred to me as a deliberate design choice.

[tahititoutou]

Thanks for this video. I've learned something.
However, I suggest you check the true meaning of the word "exponentially" in a dictionary ; the friction and inertia of a train as you add cars is not exponential, but additive. If it was exponential, event the longest draft gears would be useless past 5 or 10 cars, even with DPUs.

[nicholastrainssdm]

I remember railfanning in a train yard once and I was amazed at how many cars one GP38 could handle on it’s own even the little engines are very strong.

[cxmx]

I was starting to get worried because you haven’t been uploading for two weeks so I’m glad you uploaded and I am glad your ok.

[haulem]

Learned something today. The draft gear explanation makes a lot of sense. Will check out more of your videos.

[Mullheimer]

Physics teacher from the Netherlands here - loved it, gonne show students.

[MottyGlix]

It's not really the static friction. The use of roller bearings in the axles of all the rail cars minimizes that to irrelevance. It's the 𝘮𝘰𝘮𝘦𝘯𝘵𝘶𝘮 . The momentum of the unmoving cars is what makes the cars "want" to stay still, and what the locomotive is there to change. One rail car at a time, the locomotive is changing their momentum from zero velocity momentum to a moving velocity momentum, and *that's* when the train is put into motion.

[Steezicus]

I was an engineer for a long time and we would never use the slack to overcome the weight to get started on steep hills. Basically anything with an incline we would would stop with all the slack stretched out. The reason being all that slack running out as you start to pull will break a knuckle or drawbar.

So in theory the draft gear could help with that, but the knuckles and drawbars are not built to handle that. Draft gears are there to smooth out the slack action.

[davidcoombs]

Thought you’d find this funny. I’m an engineer for BNSF. I’m literally sitting at work right now, stopped with my train. Feet kicked up on the dash waiting for lights to pull. I have a 20, 000 ton coal load. I never really knew how these things can pull as much as they do but thanks for clearing that up lol. This particular unit is an AC4400CW and as the name implies, 4400 hp. Still it’s pretty impressive that it can pull all this weight even up hill.

[BritishBeachcomber]

The first freight wagons on British railways were limited to 14 tons because they used a horse to move them about in the freight yard and that's how much a horse can pull