| MadSci Network: Physics |
Hi Humberto!
The probable reason that the tape glows is that electric sparks are being created in the spot where the adhesive is peeling away from the layer of plastic tape beneath. I say "probable reason" because this topic is not very well researched in science. In fact, you can find an article about this in SCIENCE NEWS:
"In the peel zone: Tape's electric gooeyness," by I. Peterson, SCIENCE NEWS, Vol 146, p277 Oct. 29, 1994As I understand this, when the adhesive touches the plastic tape below it, both surfaces become electrically charged because one material steals electrons from the other. If the adhesive steals electrons, then the adhesive will have more electrons than protons (net negative charge), and the plastic tape will have fewer electrons than protons (net positive charge.) Note that no friction was involved! "Static electricity" is also known as "contact electrification", and friction is not a requirement.
When the two surfaces become oppositely charged, the electrical charges remain close together, therefor the spool of tape remains neutral (the tape contains an equal number of positive and negative charges.)
However, when you peel the tape off of the spool, you SEPARATE the adhesive from the tape below it, and this separates the regions of opposite charge. A high voltage appears between the
positive and negative charges, and this causes a "discharge" or spark to appear. The separated charges leap together through the air, and as with any spark, this creates light.
The sparking will only discharge the tape partially, and the piece of tape will remain charged, as will the surface of the tape remaining on the spool. If you peel two strips of tape from the spool, then hold them near each other, they will repel each other
(because alike charges repel, and unlike charges attract.)
This might not be the complete story. Since the adhesive forms tiny filaments as it breaks loose from the surface, perhaps some of the light
comes from burning adhesive (perhaps the tiny sparks leap along the adhesive and burn it.)
TRY THIS EXPERIMENT: take a long piece of tape and stick it to a painted metal surface, such as a filing cabinet or a refridgerator. Take a small AM radio, turn the volume up, then tune it
between two stations so you hear no signals except static. Hold the radio near the tape, then peel the tape from the metal. You will hear a crackling noise from the radio. Those sparks from the
tape are creating radio waves, and your small radio can detect them.
There are more experiments here:
Sticky Electrostatics
Try the links in the MadSci Library for more information on Physics.