Question

1.

A truck transporting petrol has a metal chain dangling to the ground
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Answer 1

Because, metallic bodies of cars , trucks or any other big vehicles gets charged because of friction between them and the air rushing past them. ... That is why tankers often have a metal chain dragging along the ground so that charge produced leaks to the ground through chain

Answer 2

Answer:

This is done to avoid the truck from watching fire. While rotating, the tyres of the truck acquire negative charge due to the movement of electrons from the ground to the tyres. As a result of this, the metal body if the truck gets positive charged. The opposite charger tyres and metal body may produce sparking which can ignore petrol and thus cause a fire.