i) Why are wheels always circular and why are they always made of rubber and not steel? (ii) What is the purpose of using shock absorbers? (Does the shape and material of the tyre have anything...
i) Why are wheels always circular and why are they always made of rubber and not steel? (ii) What is the purpose of using shock absorbers? (Does the shape and material of the tyre have anything to do with it?)
Automobile wheels are made of steel because they need to withstand a lot of hard wear. Many cars these days will hold up for two hundred thousand miles and even more. The tires mounted on the wheels are intended to make the car ride more smoothly. They also protect the steel wheels from the pavement and protect the pavement from the steel wheels. It would be impossible to have wheels made only of steel because they would tear up the streets and highways. Modern tires are no longer made of rubber but of nylon, which is tougher and longer lasting. Auto tires used to have inflated rubber inner tubes, but modern tires are tubeless.
Shock absorbers are intended to make cars ride more smoothly. A car without shock absorbers, or "shocks" as the mechanics call them, would not only give a rough ride but would cause physical injury to the spines of people who had to do a lot of driving. The shocks also protect the automobile itself, especially from a lot of jarring that could loosen nuts and bolts and lead to accidents. It is a good idea to change shock absorbers at reasonable intervals in order to protect driver and passengers--but some shops will try to sell you new shocks when you don't really need them yet.
As far as why wheels are always circular, that is because a circle is the best possible shape for the purpose. A car with square wheels or triangular wheels would give you a pretty bumpy ride. Round wheels were invented and used long before cars were even invented. In fact, a wheel by definition is round--isn't it?