Some additional questions I have to further understanding:
Ships don’t have ground, but why couldn’t electricity on a ship ground to the ocean the same way houses ground to the earth?
A structure will have a grounding rod dug into the earth. Does the dirt, soil, and rock composition that the structure is built on affect how willing current is to use the path?
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There’s nothing special about the surface of the earth as a ground. Airplane wiring, for example, has an electrical ground even though it’s flying through the air. Ground is an arbitrary reference point, but a useful one for safety.
The key idea is that electricity flows in response to *differences* in voltage between two different places. A 12-volt battery creates the same 12 volts of electrical “push” across its terminals whether it’s in contact with the ground or inside a chamber charged to high voltage.
It’s like height: if I ask you how tall you are, you give me the distance from your feet to your head. It’s the same whether you’re at sea level or on a hill. In designing a house we usually measure all heights up from the ground, taking the ground as zero elevation reference point. But one could build the same house taking measurements up from the basement or down from the top of the roof or from sea level. Won’t change the shape of the house or how much it hurts to fall off the roof.
In electricity it’s useful to define a “zero voltage” point in our circuit, so we can measure all voltages with respect to that point. This reference point is our electrical ground. It could be anywhere. But for safety, we usually measure voltage with respect to a point that people are touching or standing on: the solid earth, the metal case of the machine, or the body of a vehicle. That way we instantly know that a wire at 1000 volts with respect to that point is dangerous to anyone touching the ground,
A great demonstration of the idea that “ground is arbitrary” is workers who repair electrical lines using helicopters. They work on lines with hundreds of thousands of volts *relative to ground*, but since they’re not touching the ground, there’s no voltage difference between them and the wires they work on, so they’re fine.
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