Phawx said:
Another edit: But what does absorbing emitted frequency have to do with the impedance of the wire? And please don't link to wiki. I am being quite serious. If I have a pipe and I try to force water through it, how much water I can force through it is the impedance, as in the pipe is stopping me from putting more water through. If water starts to seep outside of the pipe I can put a sponge on the outside of the pipe to absorb excess water, but I am still able to push the theoretical amount of water through this pipe.
That is how I understand it. If I am wrong please explain.
This is a seriously complex topic. A couple of relevant links to read up for those who are interested:
http://en.wikipedia.org/wiki/Stripline
http://en.wikipedia.org/wiki/Transmission_line
Your hose pipe analogy isn't really up to the job. However, imagine the pipe is made of thin rubber, and you are not sending a steady stream of water through it, but are actually turning the tap up and down quickly. This generates pulses or water on top of a continous flow (like clock edges in a circuit). As the water comes out of the tap in a little burst, you can imagine it will stretch the rubber of the pipe (both width-ways, and maybe even length ways. I hope you can see that after flowing through a longer length of this pipe the sharp waves you put in at one end might get smeared out a bit by the time they get to the other end. You haven't lost any water, or even much energy, but the signal has been affected. Trust me - this is close enough what happens...
Now imagine you lay this pipe on top of a shallow puddle. Pulses flowing through the pipe might cause ripples to spread out through the puddle. Place another (empty) pipe close to the first one on one side, and what happens is that the ripples bounce off the 2nd pipe, maybe moving it a bit in the process, and the waves on the far side will be much smaller. This is the shielding effect which a sheet of foil buys you. now, it happens that the material surrounding the pipe does affect whats inside the pipe. If we surround our original rubber pipe with titanium tube, not a lot of signal leaks out, and maybe we manage to improve the quality of the puses we were trying to send though it. Pinch the pipe slightly to restrict it at a point, and you get reflected waves going backwards against the flow!
The key point is that a set of conductors have tiny amounts of distributed inductance and capacitance, in addition to resistance. For continous current this isn't a problem but for quickly changing current or voltage there is an effect (which is mathematically very simple, but very difficult to calculate or guess). That effect can be changed significantly by changing the conductors, or even the non-conducting material in-between.
If you imagine an inductor and capacitor connected as an oscillating circuit (a flywheel on an axle with a dot on the edge), a transmission line is almost like un-winding it, your flywheel is running across the floor.
h34r: 
