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B Why are two cellophane tapes attracted when ripped apart?

  1. Aug 22, 2016 #1
    Hello,

    I put two strips of cellophane tape adjacent to each other adhered onto a table. When I pull them both apart, they repel each other, both insulators ripped electrons from the wood.

    When I stack two strips of tape on top of each other on a table, rip the combined bundle off the table, my experiment shows that the combined piece is negatively charged on each side. Yet, when I then rip this combined piece into its two constituents pieces, they attract to each other, the top piece immediately becomes positive, the bottom piece retains its negativity. This last step is not immediately obvious to me.

    The best answer I can come up with is that more charged is ripped of the bottom sticky cellophane side from the table but less is ripped off from the top cellophane side from the non-stick bottom cellophane side, giving a net positive charge to the top cellophane tape and net negative to the bottom cellophane tape. Is that right? I draw the ideas on paper but there is always a handy-wavy gap of knowledge about how the charges distribute one step to the other. People draw these stacks as net positive and net negative yet I draw layers of positive and negative.

    P.S. When I pull two stacked pieces of tape off of a table, do the negative charges equally distribute?
     
  2. jcsd
  3. Aug 23, 2016 #2

    anorlunda

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    I think your question is a good one. Doing actual experiments, observing the results and cutthroat about the cause of the results is the scientific method.

    Unfortunately, I don't know the specific answer to your question. There were many experiments like yours, especially in the 18th century. When rubbed, some materials become positively charged while others become negatively charged. Analysis of the details depends on molecular level interactions. In most cases, we don't even know which molecules are involved. Such is the case with your tape. I don't enter know what molecules are in the tape glue.

    This Wikipedia article may help. https://en.m.wikipedia.org/wiki/Electric_charge#Electrification_by_friction. The article discusses the triboelectric effect caused by friction when two materials are rubbed. But it is not clear if that is what happens when you pull tape off.

    I hope that another PF member can give a better answer.
     
  4. Aug 23, 2016 #3
    Okay, thank you. Printed that out, looking forward to some other responses.
     
  5. Aug 23, 2016 #4

    Stephen Tashi

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    One thing to investigate is whether the two pieces of tape can function as a capacitor when stuck together - i.e is the presumed negative charge on them unequally distributed even before you pull them apart.
     
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