I'm sure you've seen them, thin little nylon looking straps that hang off the rear of a car, dragging along the ground.

What the heck are those for?? I'm in one of my curious moods...

to discharge static

Discharge static electricity buildup

the more heavy duty ones also work as a ground for the rare occasion that your car is hit by lightning ...

which really is non-sense as your car is a faraday cage anyways ... so, as long as you don't have your head sticking out the window in that thunderstorm while the lightning hits your car,
you'll be fine ...

Andy

Ground for Ham radio to make the Antenna's ground plane larger.

http://www.k2bj.com/Pages/Noise/Intro.htm