What do we mean by ground in an electrical circuit? When we want to solve electrical circuits problems, we set a "ground" level which is mean that the potential on it equal to $0$. I wonder how the current will flow if the potential at a point equal to zero.
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2This question belongs on Electrical Engineering StackExchange – Apr 06 '14 at 14:18
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The "What is ground?" question has come up on EE.SE quite a few time. See [here](http://electronics.stackexchange.com/questions/56210/what-is-ground-and-what-does-it-do), [here](http://electronics.stackexchange.com/questions/10129/when-a-battery-is-your-power-source-what-is-ground). There are more threads about ground, so don't hesitate to do some searching. – Nick Alexeev Apr 06 '14 at 18:07
3 Answers
Ground is an arbitrary definition for the (typically) lower side of a voltage differential. It's normally considered 0V, but since a voltage source is simply a difference in voltage, it's in relation to the other voltage potential. For example, two 9V batteries in series could be 18V to 0V, or can be 9V to 0V to -9V. It's all relative to what you decide is the reference voltage, aka ground.
Current flows from one voltage potential to another. If there is no difference of voltage between two points, current will not flow.

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The electricity flows from. High potential to low potential. So it can flow.Also, ground usually connect to the - of the battery. So that usually means that the ground, connect to the - of the battery.

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I agree with Passerby, but Passerby's answer describes the term neutral. There is one more use for the term ground, which differs from the term neutral - The ground should not change it's potential when a a (large) current is passed to it, the potential of the ground must be stable.

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