Guided Inquiry Why is Sticky Tape Sticky

8/17/2019 Guided Inquiry Why is Sticky Tape Sticky

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Sticky Tape Experiments

Why does Sticky Tape Find You (and Other Things) Attractive?

You are probably familiar with how invisible or sticky tape (often called “Scotch” tape) is

attracted to you and (or so it may seem) everything else when it is pulled off the roll. In this

experiment your group will explore this phenomenon in detail. Your Manager has

instructions for the part each group member will play in this experiment.

The U Tape

1. Prepare three 8" pieces of ½" invisible tape (Scotch tape or equivalent). Fold one end

of each tape under to make a non-sticky handle.

2. Stick one strip of tape to a smooth, flat surface, such as a desktop. This is your

"base" tape, and provides a standard surface on which to work, ensuring consistent

results; you will use it as the base tape for each procedure that follows. Smooth this

tape down with your thumb or finger.

3. Stick a second tape down on top of your base tape, and smooth it down well with

thumb or finger. Write "U" (for upper) on the handle of this tape.

4. With a quick motion, pull the U tape off of the base tape, leaving the base tape stuck

to the table. This action will alter the U tape so that it is attracted to other objects

(we shall say that such a tape has been “activated” and you should handle activated

tapes by their ends). Hang this activated U tape vertically from the edge of a desk or

from a horizontally mounted rod, so that it is not near any other object. This tape

should be attracted to your hand when you bring it nearby. If not, remake the U tape

and repeat the test. Record your observations.

The Interaction of Two U Tapes

5. Make a second activated U tape, and holding it by the ends, bring it near the hanging

U tape, noting how the interaction depends on the distance between the tapes. Since

both tapes were prepared in the same way, they should have the same properties.

You may find it convenient to hold the second U tape horizontally as you study how it

interacts with the hanging U tape. Record your observations.

Making a Tape Unattractive

6. Take one of your U tapes and stick the free end to the edge of the bench; with one

hand hold the tape taut and rub a finger of your other hand along its non-sticky side.

After this treatment, the U tape will no longer be attracted to other objects (we shall

say that such a tape has been “deactivated”). This is peculiar, since it would seem

that it is the sticky side that is affected by pulling the U tape off of the base tape – so

this result is a mystery. You should verify that a U tape treated this way no longer

attracts by bringing your hand up to it. There should be no attraction; if there is, rub

your thumb or finger over the smooth side again and test. Record your observations.

Making a Tape Less Attractive


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7. Rubbing your finger along part of the tape (e.g. the right half) will affect only that

part of the U tape. The interaction should be correspondingly reduced - devise an

experiment to verify that this is so. Describe what you do and record your

observations.


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The L Tape

8. There is a second way to make a tape that behaves in a similar fashion to the U tape.

To make this kind of tape, which we shall call an L tape, put a tape with a handle on

the base tape as before, but write “L” (for lower) on its handle. Next put a second tape

with a handle on top of the L tape. Label the upper piece U, for upper. You now have

three layers of tape, a base tape, an L tape, and a U tape.

9. Smooth the upper tape with your thumb or finger as before, then lift the L tape off ofthe base tape, so that the U tape comes off as well. You should observe that this pair

of tapes is attracted to other objects, much like the U tape. Stick the bottom end of

this pair of tapes to the edge of a desk or horizontally mounted rod and keeping it

taut, rub your thumb or finger along the smooth side. This should eliminate the

attractive interaction. After verifying that the pair of tapes is no longer attracted to

other things, quickly separate the pair of tapes. Record your observations.

10.You now have both a U tape and an L tape. What interaction between these two tapes

do you observe? What is the interaction of each tape with a deactivated tape?

Record your observations. At this point, hang your U and L tapes from the edge ofthe bench or support rod so that neither interacts with any other object, and proceed

with the next step.

11.Make a second U tape, as described in steps 1-4, and determine how it interacts with

the U tape you prepared in steps 8-9. What is the interaction between these two U

tapes? Is it the same as that you observed in step 5? Record your observations.

12.Make a second L tape (steps 8-9) and determine how it interacts with the first L tape.

Record your observations.

13.Repeat steps 6 and 7, substituting L tapes for U tapes. Record your observations.

What Causes U Tapes and L Tapes to Behave as They Do?

14.Your group should devise an explanation for the properties of U and L tapes. Your

theory should explain each of the following basic phenomena. Be sure to support

your conclusions with experimental observations.

P1.The interaction of U tapes with each other.

P2.The interaction of L tapes with each other.

P3.The interaction between U and L tapes.

Include in your explanation answers to the following questions:

Q1.What is the difference between a U tape and an L tape? What is your evidence?

Interlude: Discussion of Group Results and Some Background Information about the

Structure of Matter


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Activation, deactivation, and the attraction of activated tapes to ordinary objects) are more

subtle phenomena. To understand these you will need a more detailed picture of the

structure of matter, which your instructor will provide at this point.


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Extended Sticky Tape Theory

The remaining parts of this activity are to be completed by your group as homework. Your

group report is due at the beginning of the next class session.

15.Your group should extend your theory to explain each of the following phenomena.

Be sure to support your conclusions with experimental observations.

P4.Activation of U and L tapes. Why do activated tapes have different properties

than unactivated tapes - what is changed when a tape is activated?

P5.The interaction of U and L tapes with ordinary, unactivated objects. Why are

both U and L tapes attracted to unactivated objects?

P6.Deactivation and partial deactivation of U and L tapes. Why is only part, not all,

of the tape deactivated when you rub your finger over only part of the tape? Can

you explain why rubbing the non-sticky side deactivates the tape even though it

seems that it is the sticky side that is altered by the activation process?

16.On the basis of your results in this activity and the discussion inChemistry on page

1-11, predict the way that an electrically charged balloon will interact with U and L

tapes. Be sure to say what the evidence is that supports your conclusion. Do an

experiment to determine the answer and report your results.


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Instructor Notes

This activity will require 30-45 minutes for students to complete through step 13. I suggest

a break at the Interlude to have a class discussion of results and interpretations. This

discussion could be held when all groups have finished; if this is your choice, you will need

to provide activities for groups that finish early. Alternatively, you can schedule the activity

for last 30 minutes or so of class, with discussion at the start of the next class. With the

latter schedule, groups can complete unfinished work outside of class. In my own class Iwill schedule this activity for the last 30 minutes of class, then review class results and

interpretations during the first ten minutes of the next class.

After discussing group results, you can give a short lecture or lecture-demonstration on the

electrical nature of matter (Coulomb’s law, the structure of the nucleus and atom,

conductors, insulators, and induced charge separation). I use an electroscope and simple

assortment of electrostatics materials to demonstrate Coulomb’s law, induced charges, the

properties of like and unlike charges, the properties of conductors and insulators, and

charging by contact and induction (details of these demonstrations and background

information are provided below). The remaining activities can be assigned as homework.

Necessary Supplies

One roll of “invisible” tape for each team.

One balloon for each team.

Electrostatics Demonstrations

The Physics Department in your school will very likely have all of what you will need for

this set of demonstrations. If you are nice to them, they will very likely let you borrow what

you need. If there is no Physics Department or if you don’t want to be nice, you can

purchase what you need from most science supply houses. Radio Shack is an inexpensive

source of things electrical.

And remember: be sure to practice with these demonstrations just before class trying them

out in class! Humidity can conspire to make nothing work right. If this is the case,

postpone the demonstrations for a later day. When this happens to me, I simply tell them

the facts, and show them the demonstrations on a day when they work.

Necessary Equipment

A battery, flashlight bulb (one that will light, but not burn out the battery), and plastic ruler.

A battery holder with connecting wires is convenient, as is a light bulb socket.

An electroscope, the larger the better.

Thick glass rod, 6-12 inches long.

Thick Lucite rod, 6-12 inches long.

Piece of rabbit fur.

Piece of silk.


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Plastic comb.

Wire or other metal objects.


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Useful, but Not Necessary Equipment

An electrophorus, for nearly bulletproof static charge generation. A given electrophorus will

become charged either positively or negatively; you can charge by contact or induction to

produce positive and negative charges on the electroscope.

A hair drier, for those muggy days when nothing about static electricity seems to work.

Heating your apparatus will dry it out and (maybe) make it work right.

Background Information on Conductors and Insulators

Atoms are made up of a nucleus at the center and electrons that occupy the space

surrounding the nucleus. The nucleus is composed of protons, each of which has a positive

electrical charge, and neutrons that weigh about the same as protons (or about the same as

a hydrogen atom) but have no charge. Each electron has a negative electrical charge that

has the same magnitude as the positive charge on the proton; however, the mass of an

electron is only about 0.0005 times that of a proton or neutron. In a neutral atom there are

as many electrons as protons. Macroscopic objects are normally electrically neutral; there

are as many electrons in all (to a very good approximation) as protons in the atoms or

molecules of the object.

Demonstration 1: Use wires to connect the flashlight bulb to the battery. The bulb lights.

Interpose a plastic ruler between the wires and the bulb. The bulb does not light. (You may

want to have students do this for themselves. An interesting approach is to give each team

a battery, a flashlight bulb, a wire, and a plastic ruler, then ask them to make the bulb light.

When they have figured out how to do that, ask them make the ruler a part of the circuit.)

Question for the class: What can we conclude from this experiment?

Moving charges are necessary for an electric current to exist. The atoms in a solid are fixed

in position and cannot move; this means that the protons in the nucleus are not involved incarrying electrical currents in solids - they cannot move. Our demonstration shows that

something that carries what we call electrical current is able to move in conductors, such as

metal wires, but not in insulators. Experiments show that in metals there are “conduction”

electrons that are able to move freely about in the conductor. In general, there is one

conduction electron for each metal atom.

With insulators, such as plastic, each electron is bound to an individual atom or molecule

and cannot move freely through the insulator.

The Electroscope

A typical electroscope is constructed with a conducting case with glass windows and a

conducting post with foil leaves on the end enclosed by the case. The post is electrically

isolated from the case by an insulating grommet or some other device. When the leaves of

the electroscope have an electric charge, they move apart. The charge on the leaves may be

static (when the electroscope has a static charge on it) or temporary (when there is

polarization of the post and leaves induced by a nearby charged object).

You can discharge an electroscope by simultaneously touching post and case with your

fingers.


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Demonstration 2: Use the electroscope to show that rubbing the Lucite rod with fur causes

it to become charged - when brought near the post of the uncharged electroscope the leaves

move apart (if the leaves are already separated, the electroscope is charged; you should

discharge it). Rubbing the glass rod with a silk cloth causes it to become charged, for it too

causes the leaves of the uncharged electroscope to move apart. (Note: do not bring either

rod too close to the electroscope - you want to avoid charging it at this point!)

Questions for the class: How can you explain the movement of the leaves of the

electroscope? Why do they move farther apart as either charged rod is brought closer?

Each rod becomes electrically charged. When brought near the electroscope post, electrons

in the metal parts of the electroscope will be attracted toward a positively charged object or

repelled by a negatively charged object. In either case, the metal parts of the electroscope

will become polarized: one end will become positively charged, the other negatively charged.

These charges are said to be “induced” by the charged rod.

Thus, for example, if the rod is positively charged, electrons in the metal parts of the

electroscope will be attracted toward the rod so that the charge induced on the metal parts

close to it will be negative; this movement of electrons leaves the metal parts farther from

the rod with a deficiency of electrons and a positive charge. In either case, the induced

charges on the light foil leaves of the electroscope repel each other and the leaves move

apart.

Coulomb’s law describes the interaction of point charges:

Felectrical = k

1 2

2

12

QQ

R

In this expression Felectrical is the force (a push or a pull) between two charges Q1 and Q2 that

are a distance R12 apart; k is a proportionality constant whose magnitude depends on theunits chosen for charge and distance.

As we bring a rod with charge Q1 on it toward the electroscope, the separation between the

charge on the rod and the electrons in the metal parts of the electroscope decreases. As a

result, the induced charge on the leaves increases, the repulsive force between the leaves

increases, and they move farther apart. Moving the charged rod away leads to a reduced

charge on the leaves, and they move closer together.

Demonstration 3: Charging by contact. Touch the charged glass rod to the uncharged

electroscope; the leaves move apart; when the rod is removed the leaves move closer

together, but remain separated. Bringing the charged glass rod near causes the leaves tomove farther apart, but when the rod is removed, they resume their previous separation.

After discharging the electroscope, repeat this process, substituting a charged Lucite rod for

the charged glass rod. The results should appear to be the same.

Charge the electroscope by contact with the glass rod, then bring a charged Lucite rod near

the post. The leaves move closer together, but resume their previous separation when the

Lucite rod is moved away. Repeat this process, but charge the electroscope with a Lucite

rod and bring a charged glass rod near the post.


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Questions for the class: Why do the leaves of the electroscope move farther apart when

the charged rod is touched to the electroscope post? Why do they move closer together when

the charged rod is removed? What can you conclude about the charge on the electroscope

and the charge on the rod used to charge the electroscope? Why do the leaves move closer

together when you bring a charged Lucite rod (glass rod) near an electroscope that has been

charged with a glass rod (Lucite rod)? What can you conclude about the charge on the glass

and Lucite rods?

If an object becomes electrically charged, it has either lost some of its electrons and become

positively charged, or it has gained some extra electrons and become negatively charged.

When we charge by contact, as in this demonstration, a part of the excess charge on the rod

is transferred to the electroscope. If the rod is positively charged, electrons will move from

the electroscope to the rod; if the rod is negatively charged, electrons will move from the rod

to the electroscope. In either case, the induced charge on the leaves of the electroscope is

increased by this transfer of electrons, accounting for the leaves moving farther apart when

contact is made. When the rod is removed, electrons that have moved are now trapped on

the object to which they moved. Thus, when the rod is negatively charged, the electroscope

gains a negative charge, and when the rod is positive, the electroscope becomes positively

charged. The leaves move closer together when the charged rod is removed, because the

charge on the leaves is the same as that on the charged rod: increasing the separation

between the rod and the leaves reduces the induced charge on the leaves.

When you rub glass with silk, the glass becomes positively charged and the silk negatively

charged. When you rub Lucite with fur, the Lucite gains a negative charge and the fur a

positive charge. A reliable test of the sign of the charge on an electroscope, no matter how

the charge is generated, is to charge a plastic comb by passing through dry hair or rubbing

with fur or wool; it is a fact that the comb gains a negative charge. When the comb is

brought near a negatively charged electroscope, the leaves will move farther apart; if thecharge is positive, they will move closer together. You can use this simple test to determine

the sign of the charge on an electroscope and, by extension, on any charged object.

The results of this demonstration show (1) that charging by contact puts a charge on the

electroscope of the same sign as that on the charging rod, and (2) that the charge on a glass

rod is of opposite sign to that on a Lucite rod.

Demonstration 4: Charging by induction. Bring the charged glass rod close to the

uncharged electroscope (but do touch the post or come so close that a spark can jump

between the rod and post); the leaves move apart, as expected. Keeping the rod in this

position, touch the post with your finger; the leaves collapse together. Now remove your finger from the post, then move the rod away; as you do this, the leaves move apart - there

is now a net charge on the electroscope. Bring the charged glass rod close to the charged

electroscope; the leaves collapse.

After discharging the electroscope, repeat this process, substituting a charged Lucite rod for

the charged glass rod. The results should appear to be the same.

Charge the electroscope by induction with the glass rod, then bring a charged Lucite rod

near the post. The leaves move farther apart, but resume their previous separation when


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the Lucite rod is moved away. Repeat this process, but charge the electroscope by induction

with a Lucite rod and bring a charged glass rod near the post.

Questions for the class: How can you explain the differences you observe between

charging by contact and charging by induction? Specifically, answer the following

questions:

How does charging by induction work?

What is the sign of the induced charge and that of the rod used to induce the charge? How

do you know?

When you charge by induction, you take advantage of the fact that repulsions between

electrons can be reduced by increasing the distance between them. If, for example, you

bring a negatively charged Lucite rod near an uncharged electroscope, electrons in the metal

parts of the electroscope will be pushed toward parts of the electroscope farther from the rod

- in this case, toward the end to which the foil leaves are attached. This creates a negative

charge on the leaves. Touching the post allows some of these electrons on the leaves to

move even farther away - onto your body, which is a conductor - and substantially reducesthe size of the negative charge on the leaves. This is why the leaves collapse together.

Conversely, if you bring a positively charged glass rod near an uncharged electroscope,

electrons will be drawn away from the leaves of the electroscope toward the end nearest the

charged rod, leaving the leaves positively charged. Touching the post allows electrons on

your body to move onto the electroscope, substantially reduces the size of the positive

charge on the leaves, and the leaves collapse together.

When you remove your hand - before removing the charged rod - electrons that have moved

on or off of the electroscope to or from your body are now trapped. The result is a net

charge on the electroscope that is opposite in sign to that of the inducing charge.

Conclusions

At the end of this experiment you should make the point that it is electrical effects that are

responsible for all of what we call chemistry. It is the attraction of electrons for protons that

must be balanced against the repulsion that exists between electrons and electrons and

between protons and protons in order for molecules to exist. It is the same interactions that

must be balanced in order for solids and liquids to form.


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Assinments!Adapted from the Instructor"s #anual for $hemistry% A &uided Inquiry, 'e, (ohn )iley, '**'+

Manager: Manages the group. Ensures that member fulfill their roles and accomplish

assigned tasks on time, and that all group members participate in activities and understand

the concepts involved. The instructor will respond to questions from the Manager only.

Recorder/Presenter: Recorder: records names and roles for the activity; records data, group

answers and explanations. Is responsible for submitting these records in the group folder at

the end of the activity. Presenter: presents oral reports to the class.

Technician: Performs all technical operations for the group, including use of calculator or

computer. Unless an activity requires more than one individual to be involved, only the

Technician performs these operations.

Reflector: Observes and comments periodically (at approximately 15 minute intervals) on

group dynamics and behavior with respect to the learning process. These observations are

made to the Manager; the goal is to optimize group performance and learning.


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Indiidual -esults and $onclusions


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&roup -esults and $onclusions

Names of group members who participated in the activity. (Circle the recorder’s name).

______________________________ ______________________________

______________________________ ______________________________

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Guided Inquiry Why is Sticky Tape Sticky