A big part of this is we measure what's important to us. As an electrician, what's important is which wire is full of angry pixies. They're technical direction of travel is far less important to my job (and my safety). When doing electronics, the direction of travel becomes quite important. So there's a different point of view.
Actually both wires are full of angry pixies, it's just that you have angry pixies in your body that match the ones in one of the wires, so you don't notice when you touch one, and strongly notice when you touch the other.
On top of that if we did not ground one side of the electrical network, you could touch either wire and feel nothing. That's called an isolated ground, and is not commonly used except in hospitals and some other specialty settings.
(If you wonder, we ground one side because if two different people both happened to touch a wire, current would flow between them using the each.)
I was under the impression that we primarily ground one side to prevent atmospheric charge and/or things like lightning strikes causing large voltage differentials to occur between power lines and grounded objects (it's probably a bit of a fire and safety risk if the wires coming into your house could be sitting many kV above earth potential).
Yes. If you have an electrical network that isn't grounded anywhere you can't get a shock from touching only one wire because there wouldn't be any current flow. If you repair electronics you might do that to a single device with an isolating transformer, or if you are a hospital you might do that to the entire building.
But at the scale of a national grid it's basically impossible to ensure that the entire grid is isolated from the ground all the time. Stuff breaks. And if the network is grounded in some far away place but not anywhere near you you get exactly the effect you describe: you have some unknown and potentially large voltage differential towards ground because the literal ground doesn't have the same potential everywhere. So instead you give up and tie one of the potentials to ground, and do that as often as viable.
For AA batteries that's true. But licking a 9V battery gives you a notable shock. Any wet skin should work to some degree at 9V, but the tongue is very sensitive so it brings the most dramatic effect.
If you lick just one, you feel nothing. You have to lick both.
However if you set things up so that one terminal of a 9v battery is grounded, and you lick the other terminal (just one), you would feel something.
(You would also have to be grounded, at 9v that would probably require barefoot on slightly wet ground. At 120v it's a lot easier to be grounded, but the principle is the same - you only feel the electricity because the ground itself provides a return path.)
Anytime electrochemistry is involved it's important. But regular electronics not very much. I think positive and negative mostly trips up people trying to use what they think is happening to explain theory. When it's not that useful most of the time.
What I could never keep straight is anode and cathode.
It's easy! Cations are positively charged, so cathodes are, uh, negatively, charged. With anions and anodes it's the other way around.
It makes perfect sense! Cations, you see, are attracted to anions. And reduced by cathodes. Anions? Attracted to cations. And oxidized by anodes.
Whereas cations are oxidized by anions, and anions are reduced by cations.
The only alternative here would be if cathodes and cations were positively charged, and anodes and anions were negatively charged. But then cathodes would reduce anions, and cations would also reduce anions. Even worse, anodes would oxidize cations, and anions would also oxidize cations.
And we can't have that. It would just be too confusing.
The other day, I was reading a chemistry book at the point where it "helpfully" listed four different mnemonics for the same thing -- cations vs. anions, or maybe it was cathodes vs. anodes, or anyway, you know, something in that vicinity.
The terms "anode* and cathode have their own problems. The cathode is that terminal of a device where positive current emanates. The (+) terminal of a batter is normally a cathode, but when the battery is being charged, it becomes an anode.
The terms anode and cathode should be burned. We don't use them much in modern electronics. E.g. we don't say that the positive power pins of a CPU are anodes, or that ground pins are cathodes.
But if you connect a 5V battery in parallel with a 4V battery, the 5 will try to charge the 4. So the (+) terminal of the 5V battery will act as a cathode, but the (+) terminal of the 4V battery as anode.
"CCD" -> "cathode: current departs"
In chemistry though, cations are positive ions and anions are negative ions.
My personal mnemonic for that is that the letter A is often used for getting the opposite meaning of words (moral/amoral, sexual/asexual), and even moreso in my native (non-english) language. Thus my brain wired itself to associate "anode" with negative. It's quite a stretch but my mind seems to form a bunch of these weird mnemonics.
Cats are more intelligent than donkeys (âne in French). Cathode is positive, anode is negative. That's how I (and probably all French students) learned it.
