Flash of lightning

Place a metal slice on dry glass, and on it a piece of hard foam plastic which you have rubbed well on your pullover. If you hold your finger near the handle of the slice, a spark jumps across.

When the negatively charged plastic is placed on the slice, the negative electric particles in the metal are repelled to the end of the handle, and the voltage between it and the finger becomes equalized. Plastic materials can become strongly charged. In warehouses, for example, metal stands for rolls of plastic are earthed, by the personnel because otherwise they often spark.