Why does putting a carriage on rails make it much easier to pull? As in, how were the first trams such an improvement from omnibuses when the same weight was still being pulled?
In: 520
Friction and pathways.
Putting something “on rails” makes a determined pathway with navigable channels. By these two metrics alone rail travel is much smoother and faster than roads…
Rails are smooth, much smoother than roads (especially roads in the past). If you go over a bump in the road, you have to pull hard to lift the weight of the thing you are pulling up and over the bump. On smooth rails, there is much less pulling up and over bumps. Additionally, steel wheels on steel rails have very low rolling resistance. When the steel deforms (just a little) at the point where the wheel and rail are in contact, most of the defamation is purely elastic, so it does not use up energy in the process of rolling. Other materials, notably rubber, deform a lot at the contact patch when there is weight on them, and the nature of the material means this deformation takes up energy. As well, there are parts of the contact area where the wheel and surface slide over one another, with a high frictional force, so energy is used up in that process. These effects are generally termed “rolling resistance”. While people sometimes say that steel wheel on steel rail have low friction, really it is rolling resistance that is the more important effect.
A huge reduction in rolling resistance, mostly. The contact patch of a steel wheel on a steel rail is very small, and the two materials compress and conform to each other to a nearly negligible level. All of that equates to very little drag. It also explains why the wheels can lock up and slide easily under braking or hard acceleration.
Another example is riding a bicycle. It’s much easier to ride on a hard surface on a bike with hard, narrow tires, like a racing bike, as compared to a soft surface on a bike with wide, under inflated tires, like a mountain bike on a beach.
Bumps use up energy.
When you roll over a bump, you are lifting the entire carriage a tiny amount. That energy has to come from somewhere. You get some of it back on the other side of the bump but not much of it.
Air filled tyres are better than solid for the same reason. Going over a bump the tyre deforms a little but that loses a lot less energy than lifting the entire vehicle.
When a car runs on a road, its rubber wheels squish slightly. This squishing takes up energy, slowing the car down.
What’s more, if the road isn’t smooth it causes the car to bump up and down, what also takes up energy.
Steel wheels don’t squish much, and steel train tracks are durable enough that they stay smooth for a long time.
An order of magnitude less Rolling Resistance. Once a train is going, it takes very little energy to keep it going.
[Great video here](https://youtu.be/4Q22pcC98hY?t=121) about why rail has remained dominant over things like maglev – in which the presenter gives a good overview of why rail is good in the first place. The really important graphic is at [3:05](https://youtu.be/4Q22pcC98hY?t=180).
Think of your feet on the fwoor in our house. The wood fwoor is swippery, and the carpet is less swippery. Your bare feet are less swippery than your feet with socks, and the clothing maker helped us out by putting dots on the bottom of your socks.
Rail cars are your feet with socks without dots on top of the wood floor, and that’s why I can push you around without your feet even moving. It’s also why you can run and slide on your socks on the wood fwoor. Tires on concrete are your bare feet on the carpet, and you only fall down there because you are bad at staying on your feet and you enjoy falling down.
Actual ELI5: Take a soccer ball, put it on a mattress and roll it along with your hand pushing down.
The effort you have to put in isn’t that much but it is a LOT more than if you set it on a hardwood floor and push the same.
Now imagine you used a wooden ball. (Don’t do it on a hardwood floor please).
The mattress would resist a bit more but the hardwood floor it would practically glide.
The principle is the same.
The ground “feels hard” but only to a foot or hand. To the wheel of a cart it might as well be the mattress. Whilst you can roll it along it still will buckle under it and will take more effort.
The steel rail behaves like the hardwood floor.
Steel rails are very hard. When wheels roll on a flexible surface, it’s like they are always rolling uphill. When the surface flexes, the contact patch of the wheel sits at the center of a slight dip. When it rolls, it has to climb from the bottom of that dip, which is equivalent to going uphill.
This is also the reason why it makes sense to replace wooden railroad ties with concrete ties. Wood is more flexible than concrete, so the whole rail gets pressed down more when it rests on wooden ties. Since the ties ahead of the train aren’t being pressed down, this means there always exists a small uphill grade ahead of a train rolling on a track with wooden ties.
Rails have far less drag than rubber wheels.
The downside is that rail carriage are heavy, and can’t go everywhere, they need tracks.
Given that you need a strong push to accelerate, and power to keep the speed; given that early engines and horses had very strong traction but low power, rails literally changed the world. They allowed this early engines or horses to do just the acceleration work, and then keep the speed with minimal power usage (horses get less tired and steam engines consumed less of the precious coal)
Now that engines have higher power, keeping the speed is not the biggest concern, so we revert to the less efficient but more flexible wheel on road, at least for the most mundane uses.
Between this two eras, there was a time where another logic was applied: we already have the rails, let’s keep using them. Once the rails were worn down, which takes half a century or more, instead of redo the rails we scrapped them and implemented cars/trucks/buses.
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