How many types of electrical charge are there and how do they interact with one
Plastic straw, paper bits, styrofoam coffee cup, an assortment of cloth.
1. Tear a piece of paper into small bits. Place the plastic drinking straw close to the
bits of paper. Can you lift the bits of paper by touching them with the straw?
2. Now rub the straw briskly with wool or fur and place it near the bits of paper.
3. Repeat this using the styrofoam coffee cup. Try to lift the paper bits before and
after rubbing the cup on wool, fur or your own hair.
Describe the affect that the materials that have been rubbed with
wool, fur or your hair have on the paper bits?
Apparently, after the straw has been rubbed there is an interaction between the straw and paper which is capable of lifting the paper bits.
What can you say about the size of this interaction compared to that
of the Earth's gravitational interaction with the paper bits?
What can you say about the relationship between distance and this
How do the paper bits react when the straw is held at a distance?
When the straw is brought near the paper bits?
The force involved in this interaction is called an electrical force, and was first
observed by the Greeks, who found that pieces of amber(in Greek elektron)
attracted other things after being rubbed with fur. If a material attracts the
bits of paper, then it is said to be electrically charged.
1. Can you conclude at this time that the unrubbed bits of paper are charged?
2. Why might you think so?
3. Are they charged according to the definition above? How could you test for this?
4. What did you find?
1. Stick a 20 cm piece of transparent tape to your desk, leaving a tab hanging loose
over the edge of the desk.
2. Rub the tape firmly against the table.
3. Carefully remove the tape from the table by pulling up on the loose tab.
4. Slowly bring the non sticky side of the tape close to the paper bits. Record your observations: Do either or both sides of the tape attract
the paper bits like the straw or foam cup did?
Does the tape seem charged
5. Roll a piece of paper to form a tube and bring it near the tape. Is there an
interaction between the paper tube and the tape?
6. Make two charged strips like you did the first one. Try bringing the tapes near
each other and see what effect they have on one another. Does it matter which
sides of the tape face each other? Why do you think this happens?
How do the tapes react to the charged straw when it is brought near
the tapes? How would you modify the first definition of a charged
object to adequately explain this interaction?
7. Charge a third piece of tape in the same manner as the others and observe the
interactions between this tape and the other two tapes. Record your
8. Make a stand by taping the long end of a flexible straw to an upside down foam
cup. Bend the top of the straw horizontal and stick one of the three strips that you
have charged to the straw so that it hangs down. We will call this the test
9. Charge two new tapes in the following manner. Stick a piece of tape to the desk
as before. Stick a second piece of tape on top of it. Rub them well against the
surface. Peel this pair, still stuck together, away from the desk. Bring them near
the test tape.
What do you observe?
10. Bring them near the paper bits.
What do you observe? Is the combination tape charged under your
11. Now run the non sticky side of the tape across your fingers or across a water
pipe. Test the combination tape again against your test tape and the paper bits.
What do you observe in each case? Does the charged object seem to
be charged according to your definition? If it seems charged, is it
12. Carefully peel apart the tapes. Hold one in each hand and bring them slowly
towards each other. What do you observe?
13. Bring the tapes one at a time near the suspended test tape and the paper bits.
Record your observations. Can you tell with certainty from this
experiment that both the tapes are charged according to your
definition? Why or why not?
14. Suspend each of these tapes and bring a charged straw near each. Roll a piece
of paper to form a tube and bring it near the tapes. Record your observations?
Is there an interaction between the paper tube and the tapes?
1. How do your observations in this experiment allow you to extend or refine your
definition of an object being charged? Write a revised definition.
2. How do tests for attractive and repulsive interactions compare in effectiveness as
a test for objects being charged? Would either test alone be sufficient? If so
which one and why? If not, why not? Explain your reasoning.
3. How many types of charges were you working with in this activity? How do
4. If a third charge existed, how would it affect the two oppositely charged tapes in
5. Why do you think the charged straw affected the two suspended tapes as it did?
6. How would you explain the attraction or repulsion between each of the
suspended tapes and the uncharged paper roll?
7. How would you explain the fact that a charged straw can attract an uncharged
object like paper bits?
8. You actually created an electrical charge on the tapes and straw. In light of what
you have learned about atomic structure, do you think that electrons or protons
were being moved?