electrocution - Why won't you get electrocuted with a car battery unless you touch ground and positive?

First, if you have a better suggestion for title I'm really opened to suggestions, but it is the best I came up with.

If I touch an electric line and the earth, I will get electrocuted.

However, if I touch the positive of a car battery, people told me the same thing won't happen...why is it?

It seems I need to touch the battery positive and the battery ground.

Answer

For current to flow through your body, two conditions must be met:

1. There must be a complete electrical loop. Static electricity excluded, electricity only goes somewhere if it has a path to come back. Electric lines are grounded in multiple locations. Your car battery isn't.


2. The voltage must be high enough to go through your skin, which is a weak electrical barrier. For a dry skin, a ballpark figure is 20V.

Touching only the positive post of a car battery, none of the two conditions are met.