Magnetism Page 1

MAGNETISM

Permanent Magnets Magnetism ....... ............ ............ ............ .......... 2 Magnets--What Are They Good For? ..... .......... 3 Magnetic Attraction ...... ............ ............ .......... 4 Magnetic Fields ............ ............ ............ .......... 5 Magnetic Poles. ............ ............ ............ .......... 6 The Earth is a Magnet... ............ ............ .......... 7 Magnetic Mystery #1 .... ............ ............ .......... 8 Magnetic Mystery #2 .... ............ ............ .......... 9 Make Your Own Compass......... ............ ........ 10 Make Your Own Magnets.......... ............ ........ 11 Demagnetizing a Magnet ........... ............ ........ 12 Magnetic Strength......... ............ ............ ........ 13 Magnetic Levitation...... ............ ............ ........ 14 Magnetic Shielding....... ............ ............ ........ 15 Mystery Needles ........... ............ ............ ........ 16 Magnetic Separation ..... ............ ............ ........ 17 Magnetic Games ........... ............ ............ ........ 18 Magnetic Fields in 3 Dimension ............ ........ 19

Bibliography

Appendix: Figures, Explanations

List of Materials Needed

Magnetism Page 2

Magnetism

Magnetism is a fascinating, mysterious, and

easily accessible topic for elementary school children to explore. Magnetism is also one of the most difficult, least-understood subjects in mod-ern physics. But don't let that concern you. There are lots of things we can do with mag-netism that all of us can understand.

In our exploration of magnetism we will learn what makes a magnet and investigate magnets of different sizes, shapes, and strengths. We will learn a basic vocabulary of magnetism. We will learn how to make our own permanent magnets, and with our homemade magnets we will make compasses, space ships, boats, and other toys. We will also learn that electricity and magnetism are related, and how to make simple electromagnets.

This set of activities is organized into two areas: permanent magnets and electromagnets. Each area is subdivided into different activities. We will not have time to do all the activities, but by the end this session you should be able to do any of the activities we have skipped.

This magnetism section contains a series of one page descriptions of a number of activities. The description is enough to get you started, but it doesn't contain all the answers. We will dis-cover many of the questions and answers as we explore. (In science, discovering what the ques-tions are is as important as finding the answers.) The activity sheets fulfill several purposes. They help you get started with the activity, and they should be used to record your observations as you proceed. We have set aside some space for you to record any pitfalls you may notice. That way you can save yourself and others future grief.

There is a section on each activity sheet titled "Classroom Use." Only you know best how you can use (or not use) the material we present. One of the goals of this workshop is to develop lesson plans based on our activities. The activity sheets plus the filled-in section on "Classroom Use" make up the core of a lesson

plan. We would also like to know what grade level you think the activity is appropriate for.

All of these activities will help you satisfy the new Show-Me Standards. Each activity includes a list of the "performance" standards (also called Goals) and "knowledge" standards which the activity will help you teach.

There is also a section on each activity sheet marked "Comments." We want to know what you think of these activities. If an activity is the greatest thing since peanut butter, let us know. If an activity is confusing, dumb, or ridiculous, let us know also, and don't spare any harsh words. At the end of each lesson, or of each day, please copy your comments to the feedback forms we will provide, so we have access to them after you leave.

Books on activity-based science are available at most public libraries and book stores. Jane Haskell of Rolla Middle School has ordered many of them for her school library, and may be able to direct you to sources of books. We also have a number of books and science kits avail-able at this workshop. You may check them out and take them home while you are here. In reading these books, you may find that there are many activities, but only a few unique ideas, which most of the books contain. The books differ mainly in how they dress up the ideas for presentation. Following the magnet activity sheets is a list of books we have used in prepar-ing this material. A few of the activities bor-rowed heavily from particular books. In those cases, the books are cited on the individual activity sheets.

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Magnets--What Are They Good For? Materials Needed : Your thinking cap. Concepts : Applications of magnets. Activity : Group discussion. Make a list of places where magnets are used. How many can you come up with? If you're stuck, try looking around. Special Care : Please write down any pitfalls you notice. Do any parts of this activity require special care? Classroom Use : How would you use this activity in your classroom? Comments : Write down your comments on this activity. Suggested Grade Level : Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

Magnetism Page 4 Magnetic Attraction Materials Needed : Magnet, your imagination. Concepts : Magnets attract some objects but not others. Activity : Magnets will attract or be attracted to certain materials, and not to others. Before you start this activity, fill in the blanks (to the best of your current knowledge):

Magnets are attracted to . Magnets are not attracted to .

Use your magnets to make a list of those things which attract and those which do not attract. A suggested format with examples is given below. Use the back of this sheet if necessary.

Object

Composition of Object

Attracts?

Comments

soft drink bottle

glass

no

car key

metal

yes

house key

metal

no

looks like brass

After you complete this exercise, review your answers to the fill-in-the-blank questions above. Were you right? Special Care : Please write down any pitfalls you notice. Do any parts of this activity require special care? Classroom Use : How would you use this activity in your classroom? Your Comments : Grade Level : Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

Further Investigation : Just what is a magnet made of?

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Magnetic Fields Materials Needed : Magnets, iron filings, one or more compasses, paper plates. Concepts : Magnets are surrounded by a "force field." Activity : The action of a magnet is rather mysterious, isn't it? We have seen that magnets can attract objects even from a distance. Let's learn about this "force field" around a magnet.

• Put one or more magnets underneath a paper plate. Sprinkle a small amount of iron filings on a paper plate. Describe what you see. Try it with a bar magnet with N and S poles. Could you use the pattern in the iron filings to draw a picture of a magnetic field?

• With a magnet in place underneath the plate, hold a compass just above the iron filings. Which way does the compass needle point? Slowly move the compass around, just above the iron filings. What does the compass needle do? Do you see any correlation between the direction the compass needle points and the pattern of the iron filings?

• You can also sprinkle your iron filings on stiff paper (such as index cards) or glass or plastic sheets. Special Care : Please write down any pitfalls you notice. Do any parts of this activity require special care? Keep iron filings out of the eyes. Do not dip magnets directly into the filings (children are guaranteed to do this). Classroom Use : How would you use this activity in your classroom? Comments : Please write down your comments on this activity. Suggested Grade Level : Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

Magnetism Page 6 Magnetic Poles Materials Needed : Magnets. Concepts : Magnets have north and south poles. Activity : You may already know that all magnets have north and south poles. You probably noticed the "N" and "S" markings on the bar magnets we used in the Magnetic Fields activity. You also observed the presence of these poles during the iron filings experiments. Let's experiment with the idea of magnetic poles a little more. Take the different magnets you have and hold them close together in a variety of orientations. Describe what happens. Do magnetic poles always have to be at the ends of a magnet? Can you find the poles of all of your magnets?

• Experiment with some magnetized nails/pins/straightened out paper clips. Can you find the poles? • Take two magnetized nails or pins and lay them on the table parallel and close together, but with opposite poles next to each other. Slowly move one towards the other. What does the other one do? Now do the same but with like poles next to each other.

• Is it possible to make a magnet with only a north pole? With only a south pole? Could you devise an experiment to test your answers? Special Care : Please write down any pitfalls you notice. Do any parts of this activity require special care? Classroom Use : How would you use this activity in your classroom? Comments : Write down your comments on this activity. Suggested Grade Level : Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

Further Investigation : Try to make a magnet with only a north or south pole. Use a compass to find out what happens.

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The Earth is a Magnet Materials Needed : Styrofoam ball, colored toothpicks Concepts : The earth acts like a large, weak magnet. Activity :

• Stick a blue toothpick in your ball to represent the earth's geographic north pole. Stick a red toothpick in your ball to represent the earth's geographic south pole.

• Check: does everybody's earth look OK so far? • Stick a yellow toothpick in your ball to represent the earth's magnetic north pole. Stick

a green toothpick in your ball to represent the earth's magnetic south pole. • Compare "earths." Whose earth best represents reality?

Special Care : Please write down any pitfalls you notice. Do any parts of this activity require special care? Classroom Use : How would you use this activity in your classroom? Comments : Write down your comments on this activity. Suggested Grade Level : Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.

Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1. Further Investigation : Get a globe depicting the earth. Explain why the globe is oriented as it is. Have the earth's magnetic and geographic poles always been aligned? Discuss the consequences of your answer. Use foam balls and toothpicks to model the earth in your classroom.

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Magnetic Mystery #1 Materials Needed : Compass. Concepts : How a compass works. Activity :

1. Without using your compass, try to decide which direction is north. Note that direction; but don't use your compass to figure it out.

2. Put your compass on the table in front of you.

3. Compasses are generally made with a colored end which points north, and a non-colored, or maybe silver end, which points south. Look at your compass, observe which direction is north, and stand by your compass with your right arm pointing north. No cheating. Don't point some direction just because your neighbor points that way--they might be wrong!

4. Do you see anything interesting?

5. Have I made any statements which might be false?

Special Care : Please write down any pitfalls you notice. Do any parts of this activity require special care? Classroom Use : How would you use this activity in your classroom? Comments : Write down your comments on this activity. Suggested Grade Level : Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

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Make Your Own Compass Materials Needed : Nails, pins, paper clips, water containers, water, corks, styrofoam cups, aluminum foil, scissors, detergent. (Not all of these are needed.) Concepts : Needle shaped permanent magnets are used to make compasses. Activity : Make a compass based on one of the three following designs. (1) Cut off thin slices of corks; (2) cut off the bottom quarter inch or so of a styrofoam cup; (3) fold a small piece of aluminum foil in the shape of a boat. Magnetize your nails/needles/paper clips. By now you should know how to magnetize them so that they have both north and south poles. Place them on the cups/corks/boats in a container of water. If they tend to float to the side of the container, add a little detergent to the water (do you know what the detergent does?).

• What do your floating magnets do? Do you notice anything unusual about the direction in which they point? Use a bar magnet to help answer the last question.

• Do you know of any other designs for a homemade compass? Special Care : Please write down any pitfalls you notice. Do any parts of this activity require special care? If you are teaching young children, you should probably avoid using pins, knives, or razor blades. Classroom Use : How would you use this activity in your classroom? Comments : Write down your comments on this activity. Suggested Grade Level : Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

Further Investigation : Exactly how does one use a compass?

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Magnetic Mystery #2 Materials Needed : Bar magnet, compass. Concepts : North and south poles. Activity : The following questions will lead you through this activity. Answer them one at a time. Consider your answers carefully; there are no tricks, but correct logic is necessary. Complete steps 1 through 6 first. We will discuss the results together before we proceed further.

1. Fill in the blanks: magnetic poles attract and magnetic poles repel. 2. True or false: a compass is just a magnetized needle floating on a low-friction bearing. Circle one: true false. 3. The earth's geographic and magnetic poles nearly coincide. Therefore the needle of the compass that points north (i.e., is attracted to a north magnetic pole) is actually the needle's magnetic pole. 4. The colored end of your compass needle points north. Therefore, that end of the compass needle is actually the needle's magnetic pole. 5. A bar magnet has N and S poles at each end. The end of the bar magnet labeled "N" is the bar magnet's magnetic pole. 6. Experiment with your bar magnet and compass. Observe how the compass needle "follows" the bar magnet. Caution: if your bar magnet is powerful enough, it is possible to demagnetize and then remagnetize the compass needle so that its magnetic poles are switched. Before you continue, double-check that the answer you gave to (4) is still correct: the colored end of your compass needle points north. Therefore, that end of the compass needle is actually the needle's magnetic pole. 7. After you complete (6), fill in the blanks: the colored end of the compass needle is attracted to the end of the bar magnet labeled ("N" or "S", fill in one). 8. Is there anything interesting about your results? (There should be.) Can you explain your results? If you can't, do one of the following:

•Get your local high school physics teacher to explain. •Get a local college or university physics professor to explain. •Carefully repeat the experiment, have faith in your logic, and believe your results. There is a logical explanation. •Call or write me. I'll be glad to explain. •Take the UMR "Activity-Based Physical Science Class for Elementary and Middle Schools" and learn the answer there.

Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

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Make Your Own Magnets Materials Needed : Magnets, nails, needles, pins, paper clips. Concepts : Most materials which are attracted to magnets can also be made into magnets. Activity : Take a nail out of the box. Does it pick up paper clips? (See figure 1.) If it does, find one that doesn't. Now hold it against a magnet, and while maintaining contact with the magnet, see if the nail picks up paper clips (figure 2). What has happened? What have you done to the nail? Remove the nail from the magnet and see if the nail still holds up paper clips (figure 3). Repeat the above with pins instead of nails and note any differences.

• Take a nail or pin which doesn't attract paper clips. Stroke it a few times across your magnet. Now what can you do with the nail?

Fig. 1 Fig. 2 Fig. 3 Special Care : Please write down any pitfalls you notice. Do any parts of this activity require special care? If you are teaching young children, you should probably avoid using pins. Classroom Use : How would you use this activity in your classroom? Comments : Write down your comments on this activity. Suggested Grade Level : Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

Further Investigation : Many science textbooks say that in order to magnetize a nail you must stroke it in one direction only across a magnet. Is this true? What kinds of materials can you magnetize? Can you magnetize a pencil?

Magnetism Page 12

Demagnetizing a Magnet Materials Needed : Magnets, nails, pins, steel strip, iron filings. Concepts : Materials which are easy to magnetize are often easy to demagnetize. Activity : Take one of the nails you magnetized in the Make Your Own Magnets activity. Is it still magnetized? Do you know how to demagnetize it? How about the paper clips? Can you demagnetize the needles?

• Take a strip of transformer steel and hold it against a permanent magnet. Is the strip a magnet? Remove it from the magnet. Does it remain magnetized? Can you explain your results?

• Take a paper clip, hold it in contact with a permanent magnet, and pick up one or two paper clips with it (pick them up with the end not in contact with the permanent magnet, see fig. 1). Carefully remove the permanent magnet and the paper clips should remain attracted (fig. 2). Bring the opposite pole of the permanent magnet close to the first paper clip (fig. 3) and explain what happens. You can also try this with the nails and paper clips, as in the previous activity.

• Can you magnetize a jar of iron filings? Do the filings attract paper clips? What happens when you shake the jar?

• Now that you are an expert demagnetizer, can you demagnetize the needle?

Fig. 1 Fig. 2 Fig. 3 Special Care : Please write down any pitfalls you notice. Do any parts of this activity require special care? If you are teaching young children, you should probably avoid using pins. The steel strips also have sharp edges. Classroom Use : How would you use this activity in your classroom? Comments : Write down your comments on this activity. Suggested Grade Level : Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

Further Investigation : Explain how magnets become magnetized/demagnetized.

Magnetism Page 13

Magnetic Strength Materials Needed : Magnets, nails, paper clips. Concepts : Magnetic strength depends on magnet composition, size, shape, etc. Activity : Take one of your magnets. How many paper clips or nails can it pick up? Does the number of paper clips picked up depend on where they are attached to the magnet?

• If you stack two magnets together, will the pair pick up twice as many paper clips as an individual magnet? Make a prediction and then test your prediction:

Prediction: .

Result: .

Would 1000 times as many magnets pick up 1000 times as many paper clips?

• Take a different magnet, predict how many paper clips it will pick up, and test your prediction. Special Care : Please write down any pitfalls you notice. Do any parts of this activity require special care? Classroom Use : How would you use this activity in your classroom? Comments : Write down your comments on this activity. Suggested Grade Level : Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

Magnetism Page 14

Magnetic Levitation Materials Needed : Magnet, paper clips, pins, nails, tape, thread. Concepts : Magnetic force can overcome gravitational force. Activity : This works best with pins or straightened-out paper clips (cut the paper clip in half for best results). Tie 5 or 6 inches of thread to a paper clip, pin, or small nail. Tape the loose end of the thread to the table and bring a magnet close to (but not in contact with) the untied end of the paper clip/pin. What happens? Slowly move magnet around the paper clip/pin, and describe what happens.

• Can you make the pin "dance"? Can you find the poles of the magnet this way?

Special Care : Please write down any pitfalls you notice. Do any parts of this activity require special care? If you are teaching young children, you should probably avoid using pins. Classroom Use : How would you use this activity in your classroom? Comments : Write down your comments on this activity. Suggested Grade Level : Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

Magnetism Page 15

Magnetic Shielding Materials Needed : Magnets, paper clips, nails, paper, sheet steel. Concepts : Magnetic fields can pass through some objects but not others. Activity : Use your levitating paper clips/nails/pins. Devise some kind of holder for the magnets so that they levitate the pins without you having to hold the magnets; that way you have both hands free for the activity.

• Predict what will happen if you put a piece of paper (or several) between your magnet and levitating pin. Now try it. What does happen?

• Put a variety of other materials between your magnet and levitating pin. What happens? • How many sheets of paper can you put in between and still maintain levitation? How

many strips of steel? • Explain your observations. What materials do magnetic fields penetrate? What

materials act as magnetic "shields"? Special Care : Please write down any pitfalls you notice. Do any parts of this activity require special care? Classroom Use : How would you use this activity in your classroom? Comments : Write down your comments on this activity. Suggested Grade Level : Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

Magnetism Page 16

Mystery Needles Materials Needed : Two needles. Concepts : You may have trouble telling what is a magnet and what is simply being attracted to a magnet. Activity : Get two identical unmagnetized needles. Magnetize one of them. Mix them up thoroughly so you can't remember which is which. If you are tempted to "cheat" get a friend to mix them up. Is there a way to tell which one is the magnet without using any object other that the two needles themselves? Special Care : Please write down any pitfalls you notice. Do any parts of this activity require special care? Classroom Use : How would you use this activity in your classroom? Comments : Write down your comments on this activity. Suggested Grade Level : Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

Magnetism Page 17

Magnetic Separation Materials Needed : Magnet, salt, iron filings, paper. Concepts : An application for magnets. Activity : Mix together the salt and iron filings on a sheet of paper. By now you should be able to figure out how to separate the iron filings from the salt. Note the "Special Care" section below. Special Care : Please write down any pitfalls you notice. Do any parts of this activity require special care? Don't dip the magnets directly in the iron filings; hold them under the paper plate. Naturally, children are guaranteed to dip the magnets into the iron filings. Classroom Use : How would you use this activity in your classroom? Comments : Write down your comments on this activity. Suggested Grade Level : Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

Further Investigation : What else can you do with this idea?

Magnetism Page 18

Magnetic Games Materials Needed : See descriptions of games. Concepts : Here are some brief games and activities with magnets. Space Ship Docking Station . Magnetize some nails or paper clips and tie a few inches of thread to one end. Make cardboard space ships and insert the nails. Tape the "space ships" to the table around a large magnet supported on a glass or paper cup. You have made a space ship docking station. How many space ships can you dock? Magnetic Pick-Up Sticks . Clip a toothpick to a paper clip. Make several. Put all the clips/sticks in a loose pile. Who can pick up the most "sticks" one at a time without moving any of the others? You lose your turn if you move more than one stick. Treasure Hunt . Hide a prize. Have a treasure hunt. Use compass directions to guide hunters to the treasure. Floating Magnets . Insert a pencil through the holes of at least three round magnets. Can you arrange the magnets so that they float? Fishing Game . Get several long poles (dowel rods, yardsticks, real or toy fishing poles, or even tree branches will do). Tie one end of a length of thread to a magnet, the other end to the "pole." Attach "fish" to paper clips and go fishing. The fish could be: prizes, pieces of paper with questions to answer or stunts to do, etc. Another Way to Make a Magnet . Take a long steel rod. Any long (a foot or two) iron or steel rod or bolt will do. Use the compass to see if it is magnetized. Because it is steel, it should attract the compass needle. Can you tell if the rod is actually magnetized? Now hold the rod in a north-south direction, incline it at about a 20E angle to the north, and strike it a number of times with the hammer. Is the rod magnetized now? Explain why we did the above procedure. Can you guess how to demagnetize the rod? "Cutting" a Magnetic Field . Levitate a paper clip or similar object, as you did in the Magnetic Levitation activity. "Cut" the magnetic field with scissors. What really happened? Magnetic Faces . Draw a head on a paper plate. You can leave off the hair. Put a small amount of iron filings in the paper plate, cover the top with plastic wrap, and tape the plastic wrap securely all the way around. Use a magnet to move the iron filings around and put "hair" (or whatever decorations you want) on the face. Can you think of a way to preserve your masterpiece? Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

Further References : (1) Safe and Simple Electrical Experiments. (2) Teaching the Fun of Physics.

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Magnetic Fields in Three Dimensions Materials Needed : Magnets, small jar, salad oil or baby oil, iron filings. Concepts : Magnetic fields exist in three dimensions. Activity : We have already done activities where we investigated magnetic fields in two dimensions; for example, iron filings on a flat piece of paper. Now take a small jar, fill it with salad or mineral oil or something of a similar consistency, and add enough iron filings to just cover the bottom. Seal the jar, shake it up, and use some of your magnets to investigate magnetic fields in three dimensions. Another variation is to put a small magnet inside the jar along with the filings. Special Care : Please write down any pitfalls you notice. Do any parts of this activity require special care? Messy! Classroom Use : How would you use this activity in your classroom? Comments : Write down your comments on this activity. Show-Me Standards :

Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6. Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.

Magnetism Page 20 BIBLIOGRAPHY Graf, Rudolf F. Safe and Simple Electrical Experiments. New York: Dover Publications, 1973. Herbert, Don, and Ruchlis, Hy. Mr. Wizard's 400 Experiments in Science. Prism Publications, 1968. Herbert, Don, and McKie, Roy. Mr. Wizard's Supermarket Science. New York: Random House, 1980. McGill, Ormond. Science Magic. New York: Prentice Hall, 1986. Tolman, Marvin N., and Morton, James O. Physical Science Activities for Grades 2-8. West Nyack, NY: Parker Publishing Co., 1986. VanCleave, Janice Pratt. Teaching the Fun of Physics. New York: Prentice Hall, 1985. Walpole, Brenda. 175 Science Experiments to Amuse and Amaze Your Friends. New York: Random House, 1988.

Magnetism Page 21

Bar Magnet

Field From a Current Loop

Solenoid

Magnetism Page 22 Magnets--What Are They Good For?

Here are some places magnets are used: anything that has an electric motor, door latches, can opener lid holders, junkyards, automobile dealers (stick-on temporary license plates), recycling (separate iron from other metals), televisions, radios (speakers), tape recorders, vcr's, computer disks and disk drives. There are many many others. Magnetic Attraction

Only three elements are magnetic at room temperature: iron, cobalt, and nickel. There are thousands of compounds, containing more than one element, which are magnetic at room temperature, but it is a pretty safe bet that they contain iron, cobalt, or nickel. Lodestone, the naturally occurring magnet, is an iron oxide. Stainless steels contain iron; some are magnetic and others are not. Refrigerator magnets are made from barium ferrite (BaFe12O19) or strontium ferrite. More powerful alnico magnets, often used in speakers, are made of an alloy of aluminum, nickel, cobalt, and mostly iron. Samarium cobalt (SmCo5) magnets are more powerful than alnico magnets and are one of the few common magnets not containing iron. The most powerful magnets are based on Nd2Fe14B, and are made of neodymium, iron, boron, and typically small amounts of other elements.

If a magnet is attracted to something, it is a pretty safe bet that the "something" contains iron. Exceptions would be Canadian coins and samarium cobalt magnets. Magnets are not, in general, attracted to metals. Many metals are nonmagnetic: aluminum, copper, gold, some stainless steels.

We are talking permanent magnets here, of course. Later we will see that electricity can be used to create magnetism, in which case you might have a magnet attracted to something not containing iron. Magnetic Fields

Magnets are surrounded by invisible "magnetic fields." Magnetic fields are indicated using lines which, by convention, originate at north poles and end at south poles. A magnet is strongest where the magnetic field lines are most concentrated, generally at the poles. Iron filings will line up along magnetic field lines, so you can use iron filings to trace out magnetic fields.

Magnetic fields exist in three dimensions, although most books show only two-dimensional drawings. Magnetic Poles

Every magnet has a north and a south pole. This is in contrast to electricity, where you can have isolated positive and negative charges. Every magnet has both kinds of poles; you can never find a magnet with only a north or only a south pole. Physicists have theorized about the existence of "magnetic monopoles" (isolated north or south poles) but have never found one experimentally.

If you cut a magnet in half, each of the halves would be a magnet with a north and a south pole. If you cut the halves in half, you would still have magnets with both poles. If you were cutting iron, you would eventually end up with a single iron atom, which would still have a north and a south pole. If you smashed the iron atom apart, the electrons which came out would be magnets with north and south poles.

As you probably know, like poles repel and unlike poles attract.

Magnetism Page 23 The Earth is a Magnet

The earth has a magnetic field. It is theorized that nickel in the earth's core gives rise to this magnetic field. Because we have never been to the core, there are still many unanswered questions about why the earth is magnetic.

The earth's magnetic poles are located near, but not exactly at, the geographic poles. Magnetic field lines do not always point exactly north, which is why mariners using compasses to navigate need charts telling them how their compasses deviate from true north. The earth's magnetic poles actually move around in a constant, unsteady motion.

Geologists studying rocks containing magnetic materials, such as lodestone, can tell where the earth's magnetic poles were at times in the past; when a magnetic rock "freezes," it freezes like a compass needle pointing north/south. The earth's north and south poles have not always been where they are now. Of course, a small rock or even a boulder has probably moved over time; scientists use huge lava beds to map past locations of the earth’s magnetic poles.

A compass is just a small magnetic needle suspended on a low-friction bearing. The needle aligns itself along magnetic field lines, which point from north to south. Because unlike poles attract, the south magnetic pole of a compass tries to get to the north magnetic pole of the earth, and therefore points north. The colors on the compass needle have no fundamental significance. They are just paint so you can tell one end of the needle from the other. Compass makers usually try to make a colored end point north, but that doesn't have to be the case. Find out which end of your compass points north before you get lost in the woods. If you don't like the direction your compass needle points, you can always try using a powerful magnet to remagnetize the needle in the opposite direction.

Because compasses are attracted to magnetic materials and materials containing iron, they won't necessarily point north if you hold them near other magnets, other compasses, or anything containing iron (file cabinets, chairs, stools, tables with iron bolts, automobiles, etc.).

The next xxx paragraphs contain a slightly more detailed discussion of the earth’s magnetism. We will see when we study electromagnets that magnetic fields are produced by the motion of electrical charges. The magnetic field of a permanent magnet results from the motion of electrons in the atoms of the magnet. The origin of the Earth's magnetic field is not completely understood, but is thought to be primarily caused by electrical currents produced by the spinning liquid metallic outer core of iron and nickel.

The earth is made of an inner core of solid iron and nickel, surrounded by an outer core of molten iron and nickel. Outside the outer core is the mantle, a thick, dense, tar-like mixture of rocks. We live on the crust of the earth, a relatively thin layer of rocks which are less dense than the mantle and float on the mantle.

There are actually three factors which contribute to the earth’s magnetic field. The magnetic field is primarily caused by electrical currents flowing in the outer core. Natural and manmade objects in and on the earth’s crust also contribute a small amount the the earth’s magnetic field. Electrical currents flowing in upper layers of the earth’s atmosphere also contribute to the earth’s magnetic field.

The earth’s poles have reversed on average every 200 thousand years. The last time the poles reversed was about 780 thousand years ago. Are we overdue for a pole reversal? I wouldn’t lose any sleep over it; when it does happen, it will probably take place over a time period ranging from months to thousands of years.

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The earth’s geographic pole moves with time in a well-known pattern. The magnetic pole also moves. The whole story of the earth’s magnetism is very complicated, and scientists are still working hard to understand it. Magnetic Mystery #1

See the previous lesson for a discussion of the meaning of the colors on a compass needle, and the warning that compasses won't work properly if you hold them near anything containing iron.

I like this experiment because it produces a surprising result, which at first seems wrong, but has a logical explanation. In science, you get what you get. Don't "fix" the data to get an expected result. What you got might have been wrong (if that's the case, find out where you went wrong and re-do the experiment) or your interpretation might have been wrong (if that's the case, re-think). Make Your Own Compass To make a compass, simply magnetize a needle-shaped object and find a way to suspend it with a minimum of friction. Of course, it helps if your homemade compass is portable, and remember to keep it away from other magnetic materials if you want it to read accurately. Magnetic Mystery #2

I like this lesson for the same reasons that I like Mystery #1. It is correct that unlike magnetic poles attract. If we accept that geographic north is also magnetic north, then the compass needle's south pole is attracted to the earth's north pole, and points north.

The compass needle's south pole is also attracted to a bar magnet's north pole. If it is attracted to the pole labeled "S", there are several options:

(1) the experiment may have been flawed (not so in this case) (2) the bar magnet may have been mislabeled (I have seen a few that were mislabeled!) (3) the bar magnet manufacturer may have labeled the south-seeking pole with an "S", so that if you hang the bar magnet by a thread and make it into a compass, the pole labeled "S" points south, and you, the customer, are happy because the poles appear to be correctly labeled.

Make Your Own Magnets

You can make a magnet by rubbing a permanent magnet on a nail, needle, paper clip, or chunk of iron. How long your homemade magnet stays magnetized depends on its shape and how its atoms are put together. Nails tend to not stay magnetized long, paper clips are better, and it is hard to find nonmagnetic needles.

The textbooks always say "rub your nail 30 (or 20 or 40 or 60) times always in the same direction (when the moon is full and the werewolves are howling)." Actually, just touching a nail to a magnet is enough to magnetize it. Stroking it a few times might help, but don't believe for a minute that textbook authors personally check out every single statement they make. That goes for the author of these activity sheets, too. Demagnetizing a Magnet

A nail is made up of millions of tiny particles, each of which is a little magnet. In most nails, the particles are randomly aligned, the magnetic fields cancel each other, and the nail as a whole is nonmagnetic. When you magnetize a nail, you get the magnetic fields of the tiny

Magnetism Page 25 particles to line up more or less in the same direction. Any disturbance which gives the tiny particles energy is likely to demagnetize the nail. Magnetic Strength

Magnetic fields of separate magnets add together (if the magnets are aligned properly). Two identical magnets ought to be more powerful than one alone. A big magnet ought to be more powerful than a small one of the same material. A way to measure a magnet's power is how much it picks up; e.g., how many paper clips it picks up. Of course, if you magnetize the paper clips, you can't tell just how many paper clips are being picked up by the magnet, and how many are just sticking to each other.

The shape of a magnet also affects its strength. Motor designers go to great lengths designing the shapes of their magnets. A bar magnet doesn't have the right shape to give you a lot of lifting power; that's why you often see horseshoe magnets depicted as being stronger than bar magnets. Of course, the material out of which the magnet is made plays a critical role.

By the way, store your magnets just the way they "want" to be stored, and try not to drop them, because dropping them may demagnetize them. Magnetic Levitation

Magnets can lift materials which are attracted to them. If you levitate a pin (or paper clip) the pin will be most strongly attracted to the magnet's poles. Magnetic Shielding

Magnetic fields can be interrupted by materials which are attracted to magnets, such as steel, but pass through objects like your hand and paper as if they weren't there.

Mystery Needles

Hint: remember that magnets are strongest at their poles. Bar magnets can't pick up anything halfway between their poles. Magnetic Separation

Magnetic separation is a very useful technology. Try this for kicks: crush some corn flakes and see if you can pick out the iron which the manufacturer has added for your "benefit."

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Materials Needed This page contains a list of all items listed as "materials needed" for the permanent magnet activities. aluminum foil bar magnets colored toothpicks compasses corks detergent iron filings magnets nails needles paper paper clips paper plates pins salad or baby oil salt scissors small jar steel strips or sheets styrofoam cups styrofoam balls tape thread water containers (bowls) water