What Causes the Tape to Move?

Personal Lab 6

Background

We have all experienced a shock or "discharge" after shuffling our feet across the carpet, and then touching something or someone. Most of us are also familiar with the nuisance of clinging clothes after retrieval from a clothes dryer, and of "fly away" hair in the dry Arizona climate. How do thunder clouds acquire and store the electric energy that causes those spectacular Arizona lightning displays? In this activity you will explore the origin and nature of one of the most fundamental interactions in nature.

Purpose

1) To investigate what causes the tape strips to move.

2) To discover patterns in the ways that the tape strips interact with various objects.

3) To propose a model to explain the forces you observe.

Procedure

Part I: How Many Different Interactions Can You Observe?

1. Mold a small lump of clay to fit into the small aluminum dish. Poke the long ends of two flexible straws into the clay, and bend the smaller parts of each straw outward as shown in the picture.

An Electroscope
2. Tear two 4-inch strips of tape from the roll. Form a "handle" for each tape strip by folding over one end of each strip. "Prepare" the two strips by sticking them to a flat, smooth surface, such as a plastic binder or a table top, and quickly pulling the tape strips off together. Attach each strip to a straw as shown.

3. Observe what happens when you move the plastic rod and the glass rod toward each "prepared" (electrically charged) tape strip.

Try "preparing" the glass rod by rubbing it vigorously with the silk cloth, and then moving the charged rod slowly toward each tape strip on your electroscope as shown below.

Perform the same experiment with the plastic rod after rubbing it with the wool cloth. Also charge the plastic comb by drawing it through your hair 10-20 times and then moving it slowly toward the two oppositely charged tapes of your electroscope.

4. Keep a careful record your observations in a Data Table. The tape strips may lose their "charge" fairly quickly. Be sure to "recharge" the tapes by repeating procedure 2) frequently during your experiments.

5. Generate one or more hypotheses to explain the interactions you observed.

Part II: What Causes the Attraction between Objects when One Is Neutrally Charged?

1. Slowly move your finger or any other neutrally charged object toward each of the oppositely charged tapes of your electroscope. Record your observations.

2. Tear up a small part of a page of a newspaper into approximately 20 tiny bits about 5 mm in size. Spread the paper bits out on a table top.

3. Run the plastic comb through your hair (must be dry, and no mousse!) about 10-20 times.

4. Hold the charged comb a few cm above the paper bits as shown. Record what you observe.

5. Find a faucet where you can draw a small, steady stream of water as shown.

6. Run the plastic comb through your hair to charge it again, and slowly move the charged comb toward the stream of water. Record what happens.

Questions

Hand in your Data Table

1) Examine your Data Table carefully. How many types of responses of the various charged objects (e.g. plastic rod after rubbed with wool, glass rod after rubbed with silk, comb after drawn through your hair) with the oppositely charged Magic tape strips did you observe?

2) The plastic comb when drawn through your hair acquires a net negative electric charge. Was the plastic rod or the glass rod negatively charged? What kind of net electric charge did the other rod have? Explain your reasoning.

3) Did you find any conditions when the charged Magic tape strips did not react? If so, describe the conditions.

4) Was any charged or neutral object (i.e. the rods, the comb, your finger, etc.) repelled by both of the oppositely charged tape strips of the electroscope? If so, describe the conditions.

5) Were any objects (charged or neutral) attracted by both of the oppositely charged tape strips? If so, describe the conditions.

6) In the case of the experiment with the charged comb and the paper bits, what can you conclude about the relative strengths of the electric and the gravitational forces? Explain your reasoning.

7) State a hypothesis that might explain the interaction you observed between the stream of water and the charged comb.

New Terms: static electricity, positive electric charge, negative electric charge, induced polarization, electric force

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Last modified 9 Aug 1997
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