I'm very new to electronics and have been trying to learn the basics of electricity as a starting point. The mental model I've developed so far is the standard water/pipes analogy. I.e. voltage is like the pressure, amperage is flow of water, and ohms is the constricting or pinching of the pipe.
What I struggle with is how, if the circuit is open, the voltage would be unaffected by the resistors. As an example:
In this circuit if you measure the voltage between A-D, B-D, and C-D when the circuit is open like this, the voltage is always 5V. If connected however, the voltage becomes 5V, 2.5V, 0V, respectively.
Why are the open circuit voltages different? I understand that voltage represents a potential difference, but when we measure the voltage between B-D and C-D, shouldn't the resistance restrict some of that potential? It's hard for me to fit this into my mental model of water and pipes.
I know that Ohm's law requires current, and maybe that has something to do with it? But how can 5V be measured with the multimeter between C-D without the resistors affecting the potential during the measurement?