Eli5: Why train wheels don’t slip on the rails, when both the wheels and the rails are made of metal?
In: 15
The wheels are basicly a cone, then they have a flange on the inside that hold the wheel from sliding off when the wheel goes into a turn.
Friction: although both surfaces look smooth, there are minor imperfections that provide a little grip. Then, you’ve got the multi-tonne weight of the train pushing down on the wheel.
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Historically, they have, a lot.
That’s a big part of why trains can’t slow down or stop in emergency situations very well.
And why they take so long to build speed.
But modern trains typically have motors driving numerous sets of wheels all throughout the length of train (consist), so some slip while others grab and little by little as the train begins to move the slipping wheels stop slipping and begin to contribute to the momentum.
In the olden days, when there was just one locomotive dragging the entire consist, it was all about overcoming such slippage on the few drive wheels. Sand was often thrown onto the tracks by the crew to aid in traction.
But the modern approach of spreading out the driving forces via the use of electric motors makes it so that the drive wheels get a smaller amount of power and there’s more friction throughout the entire system to remedy slipping.
They do. What makes trains so energy efficient is that the friction between rail and wheel is very low. So power has to be applied very gently to stop the wheels spinning, and braking gently otherwise wheels slide.
In about 1835 they came up with the idea of dribbling dry sand onto the rails to create a bit of friction for starting and braking, and 187 years later they still do.
Modern locomotives have systems to detect slip and immediately reduce power to the wheelset that is slipping. Slipping is very hard on the wheels and the rail. Search YouTube for train slipping and you’ll find plenty of videos.
Mainly because there’s a lot of weight on the wheels. Large freight train locomotives have about 30 tons of weight on each axle. So that’s *15 tons on each wheel*.
Massive pressure helps – trains are really heavy and the contact points between rail and wheel are tiny.
They don’t slip off when going around corners because the wheels are shaped like shallow cones where the inside is slightly smaller than the outside. It’s some clever engineering. Means the whole thing becomes self centring.
OOoh boy, they do!!!! Never heard about the expression “going off the rails”?
There’s a lot of weight from the locomotive that presses down in the rails to force contact. Locos also have a lot of power to be able to move all that weight, and if that power is applied too fast they will. So the driver takes it nice and steady and off she goes. Sometimes sand is blown onto the rails to help provide friction, which is useful during starts, stops and hill climbs
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