It could be a "CV" joint, wheel bearing, ball joint, strut or any of a number of loose parts. It depends on the type of knocking and how it sounds. In any case, it should be repaired as soon as possible to avoid the possibility of a dangerous condition.
Water is wet because it is made up of a substance that feels moist when touched.
AnswerBelieve it or not but water is a bit sticky. All fluids have what we call surface tension, a tendency to stick to things even itself. You have probably notice how little objects can be stuck to the surface of water and not sink. Certain insects walk on water using this phenomina. So when you get water on yourself it kind of sticks to you. You can't shake it off, you have it wipe it away or evaporate it.
water is wet simply because the average temperature of earth promotes/preserves it to be liquid. If earth is the distance of Pluto or mercury then water here on earth would be ice or vapor then water would not be wet...you get it?
that gas to liquid problem of yours is something they call precipitation...
most elements and compounds undergoes that process too. it has something to do with their atomic mass, temperature, and other physical disturbances.
This sounds as though you mean the universe, not the world. We believe that the universe has been expanding since the big bang. As to what it's expanding into, that's something of a non-question according to astronomers. If you look around on the internet you can get detailed explanations, including one by Zogg from Betelgeuse on Youtube.
Copper can not rust there is a substance in it that may make it turn brown but then it turns green just look at the statue of liberty she is green and made of copper! Rust, by the way, is oxidized iron.