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
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.
Latest Answers