WAEC - Physics (1993 - No. 28)
A short chain is usually attached to the back of a petrol tanker and trailing behind it so that the
petrol tanker is balanced on the road
heat generated by friction in the engine can be conducted to the earth
charges generated by friction in the tanker are conducted to the earth
tanker can move slowly as the chain touches the road surface
chain can produce sound in resonance with the noise from the tanker‘s engine
Uitleg
Big vehicles gets charged because of friction between them and the air rushing past them.This is the reason tankers often have a metal chain dragging along the ground so that charge produced leaks to the ground through chain.