system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did wheels work before we invented wheel bearings?

I watched a program last night which showed a wheelwright recreating an old fashioned cart wheel and slipping it straight onto a thick wooden axle. It made me wonder just how easy it would have been to pull, and why the wheel and the axle didn't burst into flame from the friction? 

I guess they probably lubricated it with something greasy like fat, but surely that would spin off or wear away in no time? Wouldn't it just soak into the wood?

Given how ubiquitous carts were in the old days, how did they work before we invented wheel bearings?
gpt
Yes they relied on two surfaces rubbing together, and yes those surfaces were often greased. A lot (probably the majority) of rotating objects still rely on plain bearings with sliding contact like this.

Regarding the resistance, note that the sliding surface is quite a small diameter, and cart wheels tend to be very large. This means that the sliding distance for a given travel distance is quite small, so the effective resistance is quite low. This also helps to reduce wear.

Another solution to wear is to make one part sacrificial, often this is a bush or pillow block. This part is made of softer material than the other so wears faster. This can be replaced periodically, and reduces wear on the harder, retained part.

Some woods (and plastics) are also self lubricating and so prized for this purpose. For example submarines are or were until recently made with lignum vitae shaft bearings.