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.
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.
@@nicholaslau3194 well yeah, by being rubber tired they also loose the advantage of low friction while putting a lot of wear on the road (every train on exactly the same track) and tires. Is a rubber tired train more bumpy than a "normal" one? never been in one, would be interesting.
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.
I have not heard about pulsing, but in Europe electrical locomotives use a controlled slipping to achieve optimal traction (in addition to sanding). The wheels turn slightly faster as required for the speed and the traction control system ensures that the slip is in the right range.
@@janradtke8318that’s really interesting. Reminds me of how I read that when one of the fastest production motorcycles is at its ~200mph top speed, it’s rear wheel is actually turning at about 10mph faster than that due to slippage as the bike is pushing against wind resistance. It’s not directly related to your example, but still neat to think about.
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.
@@anon_148 Canadian National Railway. Back then, I was a technician for CN Telecommunications. I worked on systems for both the railway and external customers. In the mid 70s, I was based in Capreol, Ontario (near Sudbury), which is on the main line between Toronto & Montreal and Vancouver. The track between Capreol and Armstrong (North of Thunder Bay) was pretty much in the middle of nowhere, in Northern Ontario. This meant if I had work to do, anywhere along that stretch of track, I had to go by train. While there was passenger service, there were a lot more freights, so I often rode them.
@@mikehunt3420 There was also a lot of killing time, waiting for the next train. On the other hand, there were times I was sitting in the club car, having a beer, while making time & a half! 🙂
@@James_Knott Damn thats really cool. i love the railways too, and the enggineering behind them. Would be cool if you shared some stories from your career. Cheers!
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.
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.
Thank you! I’m glad you found the video informational. Ya know, that’s a good question, because snow ain’t light. I imagine in a blizzard the train wound gain at least several hundred pounds of weight.
Highly informative! I have been aware of progressive clanging of the couplers as a train goes into motion, since I was a kid. The idea of the effect of overcoming static friction one car at a time never occurred to me. It makes sense though, and your explanation made it easier to grasp the theory. Way Cool! Thank you.
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! 👍
I was a Hostler for the Rio Grande before the UP merger. We had a GE rep come in and tell us how the new GE AC locomotive could pull just as well with 5 traction motors as it did with 6. I replied that the maximum point of traction is the instant before slip. If you remove 1 motor you remove 1/6th of the contact points. The rest is either not pulling at the max or the extra #6 motor is useless. I then laid 6 dimes down on the table (representing 1 truck) and took away two to demonstrate how his promotional materials didn't jive with reality 😁
@@arda_ufukkyeah, I think there is a lot of confusion surrounding friction. Friction is completely independent of contact patch f=uN. Also, in the context of wheels, friction/traction does not equal rolling resistance. You can have infinite friction/no slipping between the wheel and the ground, but if the bearings are frictionless than the system is frictionless. Also, especially with with pneumatic tires, friction can arise from the tire deforming as it rolls. If the tire doesn’t spring back with same energy it took to deform the tire, that energy is taken from the vehicle’s momentum and lost to heat, even when no sliding occurred with the ground. This is partly why trains are so efficient, steel doesn’t deform much, but when it does, it returns almost all of the energy back into the rebound.
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!
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. 👏👏👏
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.
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.
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.
@@schoolssection Perhaps I'm wrong but I think that people in general have a tendency to utilize some words incorrectly not just Americans. Decimate is 1/10 destroyed and order of magnitude is generally the power of 10, at least as a scientist that's how I have heard it used most frequently.
are you sure static friction of 100 cars is exactly equivalent to 100 times one car? somehow i would expect more....much more. and that's probably because adding cars is adding both weight (of cars) and friction(of increased number of wheels). so i wouldn't expect linear progression.
@@ivok9846 I came here to make exactly the same point about the misuse of "exponentially". Exponentially would mean that (for example) one car doubles the static friction, the next one doubles it again, and so on, so that 10 cars would have 1,024 times as much friction. And yes, I'm pretty sure that the static friction is simply additive. Each car adds the same amount of weight and the same amount of wheels, and they are independent - the weight of one car doesn't increase the static friction of nearby cars.
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.
Hello. I'll try to be quick. There's a CSX siding behind my house here in Central Alabama. Many southbound coal trains heading to Mobile. I was able to talk shortly to the stopped engineer one time. He said he had 16,000 T behind him with no helper in the consist! 🤯 With you being with BNSF you may be familiar with the old Memphis Frisco Bridge, in operation for 130 years! And 15,000 T BNSF coal trains STILL use it! Being an OTR trucker, I've passed it many times on the I 55 interstate bridge. I'm always stunned that the bridge can still handle it. (So much for "keeping it short")
@@roadtoad7704 I actually worked as a conductor at CSX for 10 years before moving to NE for a promotion. I’ve only been an engineer for two years now but it’s definitely been a fun experience so far!!
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.
4 axle locomotives are also strong too yk. Conrail and alot of bunch of other railroads made 4 axle locomotives lead mainline trains and even intermodal trains until 6 axle widecabs replaced them.
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
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.
so, what do you do in that case? I know some extremely long rains can have 2-3 engine carts running, but how does that work? you flip them on one after the other when the "slack" comes to that part of the train?
@@TheHighborn so we apply air while all the motors are powered up to stop and that keeps it mostly stretched out (if there are DPU's there will be a little slack). Once we go to start on a hill you will power up everything to about 4-7 throttle depending on the weight and the hill. Once all the locomotives are loaded up we release the airbrakes and maybe hold the independent a little to keep from slipping. This minimizes any slack being allowed to form between the cars, but yes those DPU's that are pushing will create a little slack and you just have to be very careful to not release your air until ALL your motors are fully spooled up.
we do it here for crossings, our territory here is mostly flat with a few dips and one "step" hill (step on each side) but we have a shit ton of crossings per territory, almost double per mileage.
@@alexander1485 yeah we stop bunch up on flats for signal and crossings all the time. But your territory does not have any real grade it sounds like. The first thing you learn as an engineer when you start running trains is to always stopped stretched basically on any hill or grade. This goes for 150 unit coal trains and any length intermodal, etc. If you have to pull hard to start you simply cannot time it to pull out the slack smoothly as the air releases. Every train releases at different speeds and it even varies with temperature.
What I learned in this video. . . 1) locomotive wheel sanders, 2) overcoming static friction via coupler design, 3) close to a half million pounds of engine weight, 4) dime sized surface area between wheel and rail. Thank you for this video!
Best video I have seen in a long time. Draft gear: let me get going from a dead stop before I start pulling you.
ปีที่แล้ว +4
This is also a great explanation why it is so hard to start uphill. If you are uphill, there is no slack as the carts are trying to roll back. Unless you have fancy breaking system that would prevent them rolling when you start accelerating of course.
On North American locomotives and older euro locos (ones with lapped brakes) it's normal to start applying power as the brakes are releasing. That way you have torque applied to the wheels as the brakes come off to prevent rollback. Modern Euro locomotives simply don't release the brakes until you apply power.
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.
It is the inertia of the train that causes it to not want to accelerate(move), not momentum. Well change in momentum still requires a force, F=ma=(mv-mu)/t.
Nice wipe at 3:23 :-) This video is excellent. I'd add a few things: the very low grades that trains travel over, so that changes in gravitational potential energy is minimized. With regards to static friction, it seems you're mixing that concept with momentum. Technically the "static friction" that must be overcome is in the bearings of a train's wheels, since the wheels themselves (should) never slide on the rails. So when starting a train, momentum is the key variable (because the static friction in train bearings is very low). But the draft gear aspect was fascinating! I always assumed there was just slack between the couplers. One last point: the old fashioned steam engines and modern electric motors have one thing in common: efficiency at any RPM. Internal combustion engines do not have such efficiency. Thus a modern miracle was born: the diesel-electric. :-) Keep up the good work!
Yes he indeed mixed up concepts of inertia and static friction. Static friction between rail and wheels help the wheels to turn instead of sliding. Sliding will then produce kinetic friction. So static friction is good and don't need to be overcome and as said in video it is already quite small due to small contact area. What engines need to overcome is INERTIA.
@@wildwizardplanet Excellent, and thanks for the details! 🙂 One minor point: static friction is very large, not small due to the psi of the contact surface. A modern diesel electric locomotive has 12 drive wheels, each with a contact surface the size of a dime. The locomotive's 430,000 lb weight is spread over a small area. The huge pressure gives a healthy amount of static friction.
@@FlatEarthMath yes exactly what I meant to say is small area of contact. Of course static friction has to be sufficient and in these types of trains actually static friction of locomotives is the one that matters because only its wheels have traction motors. So they must have enough static friction to overcome inertia of whole train or they will slip. In fact they add extra weight to locomotives to achieve sufficient static friction.
@@wildwizardplanet Yes, exactly. I studied engineering in college, and we went through all the "coefficient of static friction" problems the long way. I've often marvelled at the fact that the coefficient of friction of polished steel on polished steel is quite low. But those locomotives are beasts! 🙂
For a bit of reference, I learned this particular figure when I was a kid in sixth grade! Steel wheel on steel rail, it takes 12 lbs of effort to start it rolling. Only 9 lbs is needed to keep it moving. Even though the whelk and surface are more or less solid, the minor distortion of even hardened steel means the wheel is always rolling up the slightest of inclines. MR/Trains magazine own a boxcar that is leased to some railroad or other. As an April Fool’s article, they decided to do an evaluation of it, the same as they would a scale model. By modeling standards, it was way to light. ( go figure!! ) Moving the car took a bit of effort, but not overly so. However, STOPPING it became the larger issue! Even something done in jest can teach volumes!!!
This can be easily demonstrated! "The friction of rest is always greater than the friction of motion"! Get a length of a smooth surface of your choosing. Place an object of your choosing on one end and then slowly raise that end until the object starts to move down. When your object starts moving, you will be able to slightly lower your smooth surface and the object will continue sliding down. Try it, it works.
Basically, because of the slack in the couplers, at startup you’re not actually pulling all of them at once. You move a single car, then the next one moves and so on. By the time the load gets heavy, the train is already in motion and you have momentum helping you keep it moving. It actually helps to reduce the load each coupler has as well. If they didn’t operate like that, the thousands of tons of pulling force would snap them like toothpicks.
@@mathemitelmar5546if there isn’t any static friction the wheel would be slipping. So it is not overcoming the static friction but it takes the help of the static friction to accelerate.
Never thought about the draft gear being a major reason trains can move at all. Always thought it was strictly a damper system. Absolutely brilliant...
Nicely done! I figured that there would be enough slack without a specific slack-providing mechanism, but, nope, I figured wrong. Thanks for setting me straight.
...one small detail. Friction is independent on contact area. SO no mater if thet area is like a dime, or a football field. The friction would be the same. :)
Great explanation of something that I had overlooked ie the train is almost like a long spring as it gradually stretches and finally takes full load . .
Excellent video about how trains work! Long lines of passenger cars or freight moving across the horizon are wonders to behold and now you know the secret. Note: if the locomotive is accidentally pulling on air due to a “lack of transfer”, i.e. it ain’t hooked up, then there is no way for the rest of the freight to catch up to the runaway train belching its own power and not pulling any weight. Some people incorrectly think there must be some kind of backup power plant in the rear or maybe hidden partway back mixed in with the freight so that if the workers do not actually hook up the freight to the engine at the at the front the rest of the freight will grow legs and run and catch up, pushing the freight up to speed to catch up with the runaway train. Be honest, how many of you thought that freight can just start moving by itself, engine or no engine! Or maybe each freight car has its own low power engine like a distributed network. Nope! It’s all at the front. So if it isn’t hooked up the engine has to stop, go back, get hooked up and then go on. Hopefully that doesn’t happen too late, any conductor that drives an empty train for miles before realizing it had to back up and hook up to the freight has eventually slapped themselves in the forehead and said “Oh. Right. How could I forget”, before missing every scheduled stop. It is a lesson every conductor learns just once.
Thanks for sharing this valuable knowledge, i've been living near a train station for 30 years and I just understood how it can pull this much weight, I've always thought because it's has a powerful diesel engine with so much torque but it's far more than that, especially the draft gears, simple concept yet it's a game changer
Growing up near the tracks in Johnstown PA in the early ‘50s, I remember the days of long trains starting up before the introduction of draft gears. I may be wrong, but I believe the engineers first backed up the cars, removing all slack at the couplers. Then they reversed the process, and started to pull, with a resulting “bang, bang, bang” as each successive car came under tension.
Love the combination of your sincere narration and the jazz trio. Feels like I should be preparing some red the next time I learn about trains on this channel!
I think I'm in your intro sequence! The algorithm randomly showed me this video. I was in Salina, KS (where I attended a Kansas State satellite campus) and I think that's me with the white hat on the far right watching Big Boy depart! I've never seen myself in a random video before!
I did not think I would learn anything new from this video; I just like trains. But that draft gear effect:? Wow! That makes perfect sense, and I had never thought it was important.
I have loved trains since I was a kid but I have never found a diagram or video or any type of media that illustrates how they really work in the way you described. Thank you.
Shouldn't the area of contact between the rails and the cars be inconsequential? I learnt in physics class that friction only depends on the Normal force and the nature of substances, not the area. Great video btw, I loved it!!!
Yeah this is what they teach you in high school/ 1st year university. But friction is actually a much more complicated subject and is not yet totally understood by today's engineers. But we know as a fact that friction is actually dependent on surface area because in the real world no perfectly smooth surface with a magical frictional force exists
I question whether locomotives are pulling loads that are “exponentially heavier” than themselves. That would mean the addition of one car would square the weight pulled and a third car would cube the weight pulled and so forth.
Thanks for explaining this. Always wondered about this. I thought the slack was just due to poor machining tolerances in the couplers! Now I know it's on purpose.
Timken ran a promotional film in the 1930’s where four young ladies pulled a large locomotive because of precision bearings demonstrating the rolling efficiency of train wheels.
Great presentation! And I learned something new: that draft gears in the couplers actually get the wagons to start moving more easily. Smart thinking by whoever invented it!
A wheel on a track is always stationary. So the static friction hypothesis is not all that's going on. There is static friction in all the bearings and linkages resisting the axles from starting to rotate, but then again the contact points in correctly installed bearings should also be stationary at their points of contact.
Thank you. I always wondered how they got started pulling all those loaded cars. I have train tracks running behind my apt. complex. Some are a couple of hundred cars long loaded with coal, tankers and/or containers.
I always used to think, why train couplers look so loose, every time it starts moving, makes a series of banging noises (like small bombs). But now I got it why. Thanks
Im not a train enthusiast; just a curious peruser. Had no idea about the draft gear system and that being the reason trains can pull so much weight. Thank you internet informer :D
Love the vid! I'm from Brazil, and always wandered why there aren't many trains here. The terrain full of hills explains why trains don't work so well here
video idea: i would love to see some videos on the bearings, breaks and clutch systems on trains. and thanks for this one, draft clutches are terrifying.
Recall your high school physics. The amount of friction is only dependent upon the weight and the coefficient of friction. The contact size does not play in to the equation. And, like someone said above, the bearing friction would be considerably larger than the contact friction between wheel and rail. Otherwise fine video.
Indeed, static friction is the magic behind using wheels in the first place. I believe the static friction needing to be overcome here is in the axle bearings
Wheels rolling on rails produces very little friction; it's the microscopic deflection of both wheels and rails that mimics a truck tire on soft pavement.
Well, that was interesting, and explained a lot! I work beside a large railyard, the sound of the draft gears after a car is coupled to a train is pretty cool, but until now I didn't know what they were called and what the exact purpose was.
Should also mention Rolling resistance and inertia. Friction between wheel and rail , or tyre and the road is required to start move and stop. Otherwise wheels would just spin slip under acceleration and slide skid under braking. Rolling resistance is how hard is to rotate a wheel. The biggest difference between a train wheel and a truck tyre is rolling resistance, due to the amount of flexing and distortion of a rubber tyre. The example of pushing the coffee machine , resistance to motion is friction . Train cars have wheels.. Friction between wheel and rail creates turning motion , not sliding motion.There is friction in the bearings , the resistance to train cars moving is inertia..
I've literally always wondered everything that was covered in this video. I've even looked previously for answers but nothing quite covered it this way. Especially the static friction. While this has zero practical application to my life, it's exactly the information I wanted! No longer will trains tease me with their wiles and mystery 😤
never knew there was a 'draft gear' thanks for the education, explains a lot, and trains ability to pull so many cars is what makes them so interesting.
Great informative video. I have never seen a video that explains such a complex science so simply to a layman. Also I love the friendly, folksy southern drawl. 😄
The size of the contract area should not be a factor. The formula is to multiply the coefficient of friction either static or dynamic X the normal force or weight applied perpendicular to contact surface. Dragsters with big slicks are a different story & it has something to do with rubber tires conforming or embedding themselves into the road surface.
Wow. So cool. I always thought that “slack” was just part of the couplers. It also makes the scene in the new Mission Impossible movie make more sense. They are on a luxury train that uses hooks in combination with a screw to tighten them. It seemed awfully old fashioned and unsafe compared to a modern automatic coupler.. but a heritage train is likely grandfathered in and since comfort is prioritized, they would want tight connections between cars. The light weight and low number of passenger cars would make static friction less of a concern.
How about the friction of the wheel axle on the bearing blocks? Is that a factor? Oh, and watch that "exponential". It defines a particular mathematical relationship that is not appropriate with the way you use it. Nice explanation otherwise.
![ILLSLICK - KILLSHOT REMIX [FULL VERSION]](http://i.ytimg.com/vi/RIK8RrqIAzE/mqdefault.jpg)
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"Why [sic] Locomotives Can Pull So Much" -- "How"!!!
@@rdbchasebro u good?
@@thooterhooter It's not enough for me to know the difference -- I want even TH-cam posters to!
E 0:15 0:15 0:15 eer 0:16 ee
No offense, but look up the term exponentially.
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.
Cool but probably illegal
@@Bananz-for-life-208ohh well. Can’t let the man tell you what to do all the time.
@@Bananz-for-life-208it’s a lie cuz you can’t uncouple rail cars if they’re standing still.
@@ashevilletrainman6989 you cant just drop that and not elaborate
@@ashevilletrainman6989unless it's the one on the end
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.
Most subways have traction motors under each car, so the tractive effort is distributed.
some are even rubber-tired, especially useful for steep grades
@@nicholaslau3194 well yeah, by being rubber tired they also loose the advantage of low friction while putting a lot of wear on the road (every train on exactly the same track) and tires. Is a rubber tired train more bumpy than a "normal" one? never been in one, would be interesting.
@@nicholaslau3194 Yeah, I think the Paris Metro is like that. Might be wrong though.
That's the situation in Toronto.
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.
I have not heard about pulsing, but in Europe electrical locomotives use a controlled slipping to achieve optimal traction (in addition to sanding). The wheels turn slightly faster as required for the speed and the traction control system ensures that the slip is in the right range.
shut up nigga
@@janradtke8318 Great comment, mate. Does that wear the tracks and wheels out?
@@janradtke8318 i have read that modern AC Diesel electric locos do the same thing.
Very cool that😀
@@janradtke8318that’s really interesting. Reminds me of how I read that when one of the fastest production motorcycles is at its ~200mph top speed, it’s rear wheel is actually turning at about 10mph faster than that due to slippage as the bike is pushing against wind resistance. It’s not directly related to your example, but still neat to think about.
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.
@@anon_148 Canadian National Railway. Back then, I was a technician for CN Telecommunications. I worked on systems for both the railway and external customers. In the mid 70s, I was based in Capreol, Ontario (near Sudbury), which is on the main line between Toronto & Montreal and Vancouver. The track between Capreol and Armstrong (North of Thunder Bay) was pretty much in the middle of nowhere, in Northern Ontario. This meant if I had work to do, anywhere along that stretch of track, I had to go by train. While there was passenger service, there were a lot more freights, so I often rode them.
@@James_Knott That's really cool!
@@James_Knottsounds like a hell of a job
@@mikehunt3420 There was also a lot of killing time, waiting for the next train. On the other hand, there were times I was sitting in the club car, having a beer, while making time & a half! 🙂
@@James_Knott Damn thats really cool. i love the railways too, and the enggineering behind them. Would be cool if you shared some stories from your career. Cheers!
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.
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.
Thank you! I’m glad you found the video informational. Ya know, that’s a good question, because snow ain’t light. I imagine in a blizzard the train wound gain at least several hundred pounds of weight.
@@Southern_Plains_Railfan
I would guess in some of the conditions here would easily add a ton per car. See many cars caked with ice
Highly informative! I have been aware of progressive clanging of the couplers as a train goes into motion, since I was a kid. The idea of the effect of overcoming static friction one car at a time never occurred to me. It makes sense though, and your explanation made it easier to grasp the theory. Way Cool! Thank you.
@@asds714 We generally pull into a siding before hitting Colorado, and put _snowchains_ on the drive wheels. Never notice the snow.
Back in the 70s, when I was with CN, my office was often in or next to a rail yard. I'd often hear the banging, as a train moved out.
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! 👍
Yeah, there’s a lot of neat stuff that goes on with trains, and everything feels oversized. You’re welcome!
I was a Hostler for the Rio Grande before the UP merger. We had a GE rep come in and tell us how the new GE AC locomotive could pull just as well with 5 traction motors as it did with 6.
I replied that the maximum point of traction is the instant before slip. If you remove 1 motor you remove 1/6th of the contact points. The rest is either not pulling at the max or the extra #6 motor is useless.
I then laid 6 dimes down on the table (representing 1 truck) and took away two to demonstrate how his promotional materials didn't jive with reality 😁
Friction doesn't actually depend on the contact area. The reason for the low friction coefficient is material and the structure.
@@arda_ufukkyeah, I think there is a lot of confusion surrounding friction. Friction is completely independent of contact patch f=uN. Also, in the context of wheels, friction/traction does not equal rolling resistance. You can have infinite friction/no slipping between the wheel and the ground, but if the bearings are frictionless than the system is frictionless. Also, especially with with pneumatic tires, friction can arise from the tire deforming as it rolls. If the tire doesn’t spring back with same energy it took to deform the tire, that energy is taken from the vehicle’s momentum and lost to heat, even when no sliding occurred with the ground. This is partly why trains are so efficient, steel doesn’t deform much, but when it does, it returns almost all of the energy back into the rebound.
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!
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. 👏👏👏
You're welcome! I'm glad you enjoyed!
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.
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.
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.
Yes indeed. Americans tend to be weak with numbers. "decimate" and "order of magnitude" are examples.
@@schoolssection Perhaps I'm wrong but I think that people in general have a tendency to utilize some words incorrectly not just Americans. Decimate is 1/10 destroyed and order of magnitude is generally the power of 10, at least as a scientist that's how I have heard it used most frequently.
I suppose they are using hyperbole.
are you sure static friction of 100 cars is exactly equivalent to 100 times one car?
somehow i would expect more....much more.
and that's probably because adding cars is adding both weight (of cars) and friction(of increased number of wheels).
so i wouldn't expect linear progression.
@@ivok9846 I came here to make exactly the same point about the misuse of "exponentially". Exponentially would mean that (for example) one car doubles the static friction, the next one doubles it again, and so on, so that 10 cars would have 1,024 times as much friction.
And yes, I'm pretty sure that the static friction is simply additive. Each car adds the same amount of weight and the same amount of wheels, and they are independent - the weight of one car doesn't increase the static friction of nearby cars.
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.
No need to worry about me, I just lost some footage and had to start from scratch a little late in the week. Thank you for being concerned, though.
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.
Hello. I'll try to be quick. There's a CSX siding behind my house here in Central Alabama. Many southbound coal trains heading to Mobile. I was able to talk shortly to the stopped engineer one time. He said he had 16,000 T behind him with no helper in the consist! 🤯 With you being with BNSF you may be familiar with the old Memphis Frisco Bridge, in operation for 130 years! And 15,000 T BNSF coal trains STILL use it! Being an OTR trucker, I've passed it many times on the I 55 interstate bridge. I'm always stunned that the bridge can still handle it. (So much for "keeping it short")
@@roadtoad7704 I actually worked as a conductor at CSX for 10 years before moving to NE for a promotion. I’ve only been an engineer for two years now but it’s definitely been a fun experience so far!!
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.
Yeah, I’ve seen an SD40-2 pull a mile long train all be itself, with no brakes on the cars.
Here at Conrail we do 100+ buckets with one 6 axle all the time. Shoving into the port
Little engines can do big things ;)
4 axle locomotives are also strong too yk. Conrail and alot of bunch of other railroads made 4 axle locomotives lead mainline trains and even intermodal trains until 6 axle widecabs replaced them.
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
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.
so, what do you do in that case? I know some extremely long rains can have 2-3 engine carts running, but how does that work? you flip them on one after the other when the "slack" comes to that part of the train?
@@TheHighborn so we apply air while all the motors are powered up to stop and that keeps it mostly stretched out (if there are DPU's there will be a little slack).
Once we go to start on a hill you will power up everything to about 4-7 throttle depending on the weight and the hill. Once all the locomotives are loaded up we release the airbrakes and maybe hold the independent a little to keep from slipping.
This minimizes any slack being allowed to form between the cars, but yes those DPU's that are pushing will create a little slack and you just have to be very careful to not release your air until ALL your motors are fully spooled up.
@@Steezicus that was informative. Thanks
we do it here for crossings, our territory here is mostly flat with a few dips and one "step" hill (step on each side) but we have a shit ton of crossings per territory, almost double per mileage.
@@alexander1485 yeah we stop bunch up on flats for signal and crossings all the time. But your territory does not have any real grade it sounds like. The first thing you learn as an engineer when you start running trains is to always stopped stretched basically on any hill or grade. This goes for 150 unit coal trains and any length intermodal, etc.
If you have to pull hard to start you simply cannot time it to pull out the slack smoothly as the air releases. Every train releases at different speeds and it even varies with temperature.
Physics teacher from the Netherlands here - loved it, gonne show students.
That's wonderful to hear!
Learned something today. The draft gear explanation makes a lot of sense. Will check out more of your videos.
Thank you, I’m glad you found the video informative! I hope you find some of my other videos just as informative as well.
What I learned in this video. . . 1) locomotive wheel sanders, 2) overcoming static friction via coupler design, 3) close to a half million pounds of engine weight, 4) dime sized surface area between wheel and rail. Thank you for this video!
Best video I have seen in a long time. Draft gear: let me get going from a dead stop before I start pulling you.
This is also a great explanation why it is so hard to start uphill. If you are uphill, there is no slack as the carts are trying to roll back. Unless you have fancy breaking system that would prevent them rolling when you start accelerating of course.
On North American locomotives and older euro locos (ones with lapped brakes) it's normal to start applying power as the brakes are releasing. That way you have torque applied to the wheels as the brakes come off to prevent rollback. Modern Euro locomotives simply don't release the brakes until you apply power.
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.
Came to make a similar comment.
It is the inertia of the train that causes it to not want to accelerate(move), not momentum.
Well change in momentum still requires a force, F=ma=(mv-mu)/t.
Nice wipe at 3:23 :-) This video is excellent. I'd add a few things: the very low grades that trains travel over, so that changes in gravitational potential energy is minimized. With regards to static friction, it seems you're mixing that concept with momentum. Technically the "static friction" that must be overcome is in the bearings of a train's wheels, since the wheels themselves (should) never slide on the rails. So when starting a train, momentum is the key variable (because the static friction in train bearings is very low). But the draft gear aspect was fascinating! I always assumed there was just slack between the couplers. One last point: the old fashioned steam engines and modern electric motors have one thing in common: efficiency at any RPM. Internal combustion engines do not have such efficiency. Thus a modern miracle was born: the diesel-electric. :-) Keep up the good work!
Yes he indeed mixed up concepts of inertia and static friction. Static friction between rail and wheels help the wheels to turn instead of sliding. Sliding will then produce kinetic friction. So static friction is good and don't need to be overcome and as said in video it is already quite small due to small contact area. What engines need to overcome is INERTIA.
@@wildwizardplanet Excellent, and thanks for the details! 🙂 One minor point: static friction is very large, not small due to the psi of the contact surface. A modern diesel electric locomotive has 12 drive wheels, each with a contact surface the size of a dime. The locomotive's 430,000 lb weight is spread over a small area. The huge pressure gives a healthy amount of static friction.
@@FlatEarthMath yes exactly what I meant to say is small area of contact. Of course static friction has to be sufficient and in these types of trains actually static friction of locomotives is the one that matters because only its wheels have traction motors. So they must have enough static friction to overcome inertia of whole train or they will slip. In fact they add extra weight to locomotives to achieve sufficient static friction.
@@wildwizardplanet Yes, exactly. I studied engineering in college, and we went through all the "coefficient of static friction" problems the long way. I've often marvelled at the fact that the coefficient of friction of polished steel on polished steel is quite low. But those locomotives are beasts! 🙂
What’s an “exponentially long train”? 😂😂😂😂
I had never heard of draft gear in rail car couplers. Learn something new every day! Great video, thanks!
For a bit of reference, I learned this particular figure when I was a kid in sixth grade!
Steel wheel on steel rail, it takes 12 lbs of effort to start it rolling.
Only 9 lbs is needed to keep it moving.
Even though the whelk and surface are more or less solid, the minor distortion of even hardened steel means the wheel is always rolling up the slightest of inclines.
MR/Trains magazine own a boxcar that is leased to some railroad or other.
As an April Fool’s article, they decided to do an evaluation of it, the same as they would a scale model.
By modeling standards, it was way to light. ( go figure!! )
Moving the car took a bit of effort, but not overly so.
However, STOPPING it became the larger issue!
Even something done in jest can teach volumes!!!
This can be easily demonstrated! "The friction of rest is always greater than the friction of motion"! Get a length of a smooth surface of your choosing. Place an object of your choosing on one end and then slowly raise that end until the object starts to move down. When your object starts moving, you will be able to slightly lower your smooth surface and the object will continue sliding down. Try it, it works.
Basically, because of the slack in the couplers, at startup you’re not actually pulling all of them at once. You move a single car, then the next one moves and so on. By the time the load gets heavy, the train is already in motion and you have momentum helping you keep it moving. It actually helps to reduce the load each coupler has as well. If they didn’t operate like that, the thousands of tons of pulling force would snap them like toothpicks.
Low rolling resistance not low friction. The friction coefficient of steel on steel can actually quite high
For the static case we first have to overcome static friction, after the initial movement its rolling resistance
@@mathemitelmar5546if there isn’t any static friction the wheel would be slipping. So it is not overcoming the static friction but it takes the help of the static friction to accelerate.
As a Canadian, who speaks in a hard, flat English accent, it’s a pleasure to hear that soft Southern narration.
When I was little I was completely obsessed with trains. Guess it never truly faded.
Never thought about the draft gear being a major reason trains can move at all. Always thought it was strictly a damper system. Absolutely brilliant...
Nicely done! I figured that there would be enough slack without a specific slack-providing mechanism, but, nope, I figured wrong. Thanks for setting me straight.
3:29' southern gem.
...one small detail. Friction is independent on contact area. SO no mater if thet area is like a dime, or a football field. The friction would be the same. :)
Great explanation of something that I had overlooked ie the train is almost like a long spring as it gradually stretches and finally takes full load . .
Wow, I’ve never heard static friction and exponential used improperly do many times in so little time.
Excellent video about how trains work! Long lines of passenger cars or freight moving across the horizon are wonders to behold and now you know the secret.
Note: if the locomotive is accidentally pulling on air due to a “lack of transfer”, i.e. it ain’t hooked up, then there is no way for the rest of the freight to catch up to the runaway train belching its own power and not pulling any weight.
Some people incorrectly think there must be some kind of backup power plant in the rear or maybe hidden partway back mixed in with the freight so that if the workers do not actually hook up the freight to the engine at the at the front the rest of the freight will grow legs and run and catch up, pushing the freight up to speed to catch up with the runaway train.
Be honest, how many of you thought that freight can just start moving by itself, engine or no engine! Or maybe each freight car has its own low power engine like a distributed network. Nope! It’s all at the front.
So if it isn’t hooked up the engine has to stop, go back, get hooked up and then go on.
Hopefully that doesn’t happen too late, any conductor that drives an empty train for miles before realizing it had to back up and hook up to the freight has eventually slapped themselves in the forehead and said “Oh. Right. How could I forget”, before missing every scheduled stop.
It is a lesson every conductor learns just once.
Thanks for sharing this valuable knowledge, i've been living near a train station for 30 years and I just understood how it can pull this much weight, I've always thought because it's has a powerful diesel engine with so much torque but it's far more than that, especially the draft gears, simple concept yet it's a game changer
Growing up near the tracks in Johnstown PA in the early ‘50s, I remember the days of long trains starting up before the introduction of draft gears. I may be wrong, but I believe the engineers first backed up the cars, removing all slack at the couplers. Then they reversed the process, and started to pull, with a resulting “bang, bang, bang” as each successive car came under tension.
Awesome! I found this video while researching that each persons roll is on the train. Conductor, engineer, etc.
Love the combination of your sincere narration and the jazz trio. Feels like I should be preparing some red the next time I learn about trains on this channel!
I think I'm in your intro sequence! The algorithm randomly showed me this video. I was in Salina, KS (where I attended a Kansas State satellite campus) and I think that's me with the white hat on the far right watching Big Boy depart! I've never seen myself in a random video before!
I did not think I would learn anything new from this video; I just like trains. But that draft gear effect:? Wow! That makes perfect sense, and I had never thought it was important.
I was just thinking about this topic yesterday and lo and behold, youtube recommends this video. Fantastic explanation!
I have loved trains since I was a kid but I have never found a diagram or video or any type of media that illustrates how they really work in the way you described. Thank you.
Shouldn't the area of contact between the rails and the cars be inconsequential? I learnt in physics class that friction only depends on the Normal force and the nature of substances, not the area. Great video btw, I loved it!!!
Yes, that’s what I’m thinking too.
Yeah this is what they teach you in high school/ 1st year university. But friction is actually a much more complicated subject and is not yet totally understood by today's engineers. But we know as a fact that friction is actually dependent on surface area because in the real world no perfectly smooth surface with a magical frictional force exists
@@mathemitelmar5546 oooHhhhh interesting
Also sophisticated traction control for motors aids in pulling ability of locos today.
Watching a roundhouse in action in a busy yard was like poetry in motion when I was a kid.
I question whether locomotives are pulling loads that are “exponentially heavier” than themselves. That would mean the addition of one car would square the weight pulled and a third car would cube the weight pulled and so forth.
Calling the load “an order of magnitude or more heavier than themselves” would likely be a better description.
He's not saying each car is exponentially heavier, literally. The total load some trains pull when all cars are moving is exponentially heavier.
GREAT VIDEO!!!
Absolutely LOVe the chill non contrived style.
Thanks for explaining this. Always wondered about this. I thought the slack was just due to poor machining tolerances in the couplers! Now I know it's on purpose.
Timken ran a promotional film in the 1930’s where four young ladies pulled a large locomotive because of precision bearings demonstrating the rolling efficiency of train wheels.
Don't forget body builder Charles Atlas towing a PRR Broadway Limited observation car in the late 1930s!
What about inertia and the rolling friction of the wheel bearings?
I never cared about trains but this has gotten me interested!
What a great Mechanism to solve it. Thanks for educating me.
Great presentation! And I learned something new: that draft gears in the couplers actually get the wagons to start moving more easily.
Smart thinking by whoever invented it!
A wheel on a track is always stationary. So the static friction hypothesis is not all that's going on. There is static friction in all the bearings and linkages resisting the axles from starting to rotate, but then again the contact points in correctly installed bearings should also be stationary at their points of contact.
Very informative, clear, concise! Thanks for sharing. [Greetings from Tucson.]
You’re welcome, I’m glad you enjoyed! Greeting from Illinois.
Very cool. I wish trains still existed today. Time goes by so dang fast...
Yeah, too bad all the trains caught rabies and died. Kinda flooded the scrap metal market too... but hey, at least the price of coppers gone down!
I would imagine the draft gear, coupler slack, would be more effective at incrementally dealing with delta mv or change in momentum.
Thank you. I always wondered how they got started pulling all those loaded cars. I have train tracks running behind my apt. complex. Some are a couple of hundred cars long loaded with coal, tankers and/or containers.
I always used to think, why train couplers look so loose, every time it starts moving, makes a series of banging noises (like small bombs). But now I got it why. Thanks
The draft gear is an amazing idea, so simple, yet so efficient!
The more i learn about trains, the more i love them. Seriously, trains are one of the most important inventions ever.
Im not a train enthusiast; just a curious peruser. Had no idea about the draft gear system and that being the reason trains can pull so much weight. Thank you internet informer :D
Thanks. I've known of the slack for a long time but never thought of how that aids the engines.
You answered the exact question that was burning in my mind.
Wonderful! Glad I could help.
Wow well done. I understand completely now. You are a good instructor.
Thank you!
04:20 I always heard that sound when Freight train starts moving...now I know the reason why.
I'm not overly interested in trains but this was a really concise and well put together video. Thanks
The draft gear also helps build momentum as the train advances.
Love the vid! I'm from Brazil, and always wandered why there aren't many trains here. The terrain full of hills explains why trains don't work so well here
video idea: i would love to see some videos on the bearings, breaks and clutch systems on trains.
and thanks for this one, draft clutches are terrifying.
This is a top-notch video. Well thought-out and executed.
Thank you!
Recall your high school physics. The amount of friction is only dependent upon the weight and the coefficient of friction. The contact size does not play in to the equation. And, like someone said above, the bearing friction would be considerably larger than the contact friction between wheel and rail. Otherwise fine video.
Very concise and accurate. And what a mellifluous voice to explicate it.
Thanks for explaining that. I always wondered how trains got moving from a standstill.
You’re welcome, glad I could answer some of your questions!
Thanks for the video Mr. That was really cool I walk over a railroad crossing a lot throughout my day and I didn't know anything about slack
Thanks.
Unless sliding, the wheels are always under static friction.
Rolling of any kind is static friction.
Indeed, static friction is the magic behind using wheels in the first place. I believe the static friction needing to be overcome here is in the axle bearings
Wheels rolling on rails produces very little friction; it's the microscopic deflection of both wheels and rails that mimics a truck tire on soft pavement.
Explained like I'm 5. Love it!
lol, glad you enjoyed!
Well, that was interesting, and explained a lot! I work beside a large railyard, the sound of the draft gears after a car is coupled to a train is pretty cool, but until now I didn't know what they were called and what the exact purpose was.
Wow, never knew about draft gears. I just thought that was the normal play in the connection. Never realized it was intentional! Neat!
Should also mention Rolling resistance and inertia.
Friction between wheel and rail , or tyre and the road is required to start move and stop. Otherwise wheels would just spin slip under acceleration and slide skid under braking. Rolling resistance is how hard is to rotate a wheel.
The biggest difference between a train wheel and a truck tyre is rolling resistance, due to the amount of flexing and distortion of a rubber tyre.
The example of pushing the coffee machine , resistance to motion is friction . Train cars have wheels.. Friction between wheel and rail creates turning motion , not sliding motion.There is friction in the bearings , the resistance to train cars moving is inertia..
Thanks for the video. Loved it 👍🏿. Fascinated by engineering and big stuffs...
You've very welcome, I'm glad you enjoyed!
What a great video, thank you. I don't know of anyone who doesn't love a train going by.
this guy knows physics and trains, loved the video
Huh, a draft gear, I never knew that. I always thought the slamming sound was just slop in the coupler. Who knew that was by design? Genius!
I've literally always wondered everything that was covered in this video. I've even looked previously for answers but nothing quite covered it this way. Especially the static friction. While this has zero practical application to my life, it's exactly the information I wanted! No longer will trains tease me with their wiles and mystery 😤
never knew there was a 'draft gear' thanks for the education, explains a lot, and trains ability to pull so many cars is what makes them so interesting.
Great informative video. I have never seen a video that explains such a complex science
so simply to a layman.
Also I love the friendly, folksy southern drawl.
😄
I don’t think this guy knows what the phrase “exponentially” means! 😂😂😂
Agreed... neither do many of his audience I suspect. The wt. of each car is additive...
Amazing video thoroughly enjoyed it and learned a lot!
Thank you! I’m glad you found the video informational!
The size of the contract area should not be a factor.
The formula is to multiply the coefficient of friction either static or dynamic X the normal force or weight applied perpendicular to contact surface.
Dragsters with big slicks are a different story & it has something to do with rubber tires conforming or embedding themselves into the road surface.
Wow. So cool. I always thought that “slack” was just part of the couplers.
It also makes the scene in the new Mission Impossible movie make more sense. They are on a luxury train that uses hooks in combination with a screw to tighten them. It seemed awfully old fashioned and unsafe compared to a modern automatic coupler.. but a heritage train is likely grandfathered in and since comfort is prioritized, they would want tight connections between cars. The light weight and low number of passenger cars would make static friction less of a concern.
But the links were not strong enough to take the weight of a few carriages.
*The most interesting part was about the draft gear's function. You solved a big question there.*
Yeah. I always thought that sound from the slack pulling up was just that, slack, and nothing else. Who knew.
If there was a video like this every time I got on TH-cam I wouldn’t have to Tictok anymore
How about the friction of the wheel axle on the bearing blocks? Is that a factor?
Oh, and watch that "exponential". It defines a particular mathematical relationship that is not appropriate with the way you use it. Nice explanation otherwise.
Never seen an educational video with a southern accent 😄👍🏻