Related: Why two objects get charged by rubbing?

After reading the above question’s answer given by Luboš Motl in terms of the triboelectric effect, I believe I have a good grasp on how charge is transferred between two different materials.

My question is why does plastic wrap, made of one type of material, when pulled from a roll gets one side negatively charged while the other side gets positively charged?

I was unable to understand this question after reading several links on the triboelectric effect and electronegativity. It appears to me that this effect is responsible for two different materials transferring charge but was unclear to me when speaking on how charge is transferred between the same material, as in the case of the plastic wrap. I’d appreciate any help for a correct explanation.

  • $\begingroup$ How did you know that one side of the wrap got positive and the other negative (charge)? $\endgroup$ – Immortal Player Mar 1 '14 at 17:07
  • 1
    $\begingroup$ @GODPARTICLE: If one charges a very small pith ball negatively, one side of the plastic attracts the pith ball while the other side repels it. $\endgroup$ – Carlos Mar 1 '14 at 17:53

Plastic wraps are made up of PVC. They might be cohesive (like mercury) because of their molecular shape and other chemical factors, which might cause them attract each other. When you apply force to pull the plastic wrap from the roll, this might cause the electrons from pulled surface to gain electrons and the other to loss the electrons, giving positive and negative charges on either sides.

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