| Using such everyday items as a straw, tape,
plastic pen and various types of cloth, we'll explore static electricity
and how items can be charged, discharged, and recharged. |
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You'll need a straw that
still has the paper covering on it. Carefully tear one end of the
paper and slide about one inch of the straw out of the paper.
Partially push and pull the straw in and out of the paper five times.
Remove the paper and lay it on the table while holding one end of
the straw with your fingertips. |
| Like a
wand, lower the straw and hold it next to the paper, then raise the
straw again. What happens?
Now take the straw and "wipe" it through your bare palm a couple
of times. Once again hold the straw to the paper. What happened?
Q1: When
you first pull the straw out of the paper there is a static electric
charge present. Where do you think this charge originated from?
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Q2: The Coulomb force
(attractive or repulsive force between charged objects) between
the paper and the straw allows you to initially attract the paper
and "lift" it off of the table. What must be true of the relative
sizes of Coulomb force and force due to Gravity for the paper
to be lifted by static electricity?
Q3: Why won't the straw pick up the paper after you wipe
the straw through your bare hand a few times?
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Take the straw and rub it with some cloth,
like your shirt or coat. Locate the point on the straw that you think
is about half its length. Use a long narrow piece of tape to hang
the straw from the edge of your desk. Make sure the straw can move
freely.
Hold one end of a plastic pen near one end of the straw. Does anything
happen? Now take the pen and rub it over a piece of fabric, ten
or twenty times. Again hold the end of the pen near the end of the
straw. What happens?
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| Q4: What
does rubbing the plastic pen or the straw over fabric do to the pen
and straw?
Q5: Why does the
straw "spin" when you hold the end of the pen near it? What would
happen if you rubbed the pen over a different material, like rubber
or leather and then brought the pen near the straw? See the table
of triboelectronegativities.
Q6: Draw a free-body
diagram of the paper while it is being lifted by the straw. Label
the Coulomb force and force due to gravity and indicate their relative
sizes.
Advanced Question:
What must be the minimum Coulomb force present for you to lift the
paper if you know its mass is 0.15 grams?
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