Thanks............
Here's what i'm still struggling with in terms of ground:
Attached are two pix. In the first pic, with have a leg of the circuit going nowhere, so no current through the 5k resistor.
In the second pic, i've grounded that leg, so current can flow.
Hence my understanding that ground can be used to make current flow where it otherwise wouldn't want to flow.
But by this logic one could have multiple different "ground" planes, not connected to each other. But this isn't something i've seen, therefore i surmise this isn't actually the purpose of ground.
Ok, so ground is often (also in this thread) described as being used as a "reference". This is the part i don't understand. When i think of "reference" i think of an intelligent agent referencing some information from a user manual or wikipedia or something like that. But i have no clue as to the meaning of the word "reference" as it's being used in this context.
Could someone please give me an ultra-simple example (maybe an EveryCircuit circuit) of such "referencing" taking place? (With an explanation)
I used to work at a TV Station, & on occasion had to climb the tower at the Transmitting site.
This tower was 145m high, so when I was replacing the topmost clearance light, I was that height above the base of the tower.(or "ground")
OK, I was 145m high----- but wait! the site was about 300m above sea level, so was I (145+300) metres high?
So the question is which?
Well, if we are referring to the ground at the base of the tower, it is 145m , if we are referring to the ground at the very point where the beach meets the sea, then I am 445m above ground.
Of course, the reference for height doesn't have to be the ground, either.
The CH2 tower is a bit further up the hill, & is about the same size as our one was, so I may have been about minus 4m with reference to the top of that tower.
You can see that the same vertical position in space can be different heights, depending upon where you measure them from.
You will probably have seen the initials "w.r.t"----these mean, either "with reference to" or "with respect to" which are just different ways of saying the same thing.
On top of the tower, I was 145m high w.r.t the tower base, but I was 445m high w.r.t. sea level, & around minus 4m "height" w.r.t. the top of CH2's tower.
In all cases, a word which could describe the place my height was measured from is a "reference".
As in height, so with voltage.
In your original schematic, using the point you put a "ground" symbol on as your reference, the positive terminal of the battery is 4.5v w.r.t. your reference point.
The negative terminal of your battery now becomes -4.5v w.r.t. your reference point.
Nothing has happened to your battery, if you ignore the point with the ground symbol, & hang your meter across it, you will still read 9v.