Mondo Magnets

40 Attractive (and Repulsive) Devices and Demonstrations

Fred Jeffers

• Publisher: Chicago Review Press
• Year: 2007
• Print ISBN: 9781556526305
• eBook ISBN: 9781613742440
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Physics
• Index: Physics

Surprising and seemingly impossible effects result from the 40 experiments included in this fascinating science resource—all based on real magnetic physics. Each experiment—such as using a common refrigerator magnet to create a three-dimensional image or floating a magnet and carbon sheet in midair—is outlined with step-by-step instructions and diagrams that illustrate the key concepts of magnetism. Even the most experienced science teacher or at-home tinkerer will find dozens of new tricks in this amazing collection.

Experiment 1

Magnetic Money, Rocks, Beach Sand, Total® Cereal, and Dirt

It’s shown that money, many rocks, beach sand, Total® cereal, and even common dirt are magnetic.

Materials

U.S. $1 bill

Cellophane tape

Very strong magnet (such as an NdFeB magnet)

Rock (see page 2)

Several handfuls dry beach sand

Two small, nonmagnetic jars (such as glass baby food jars) and their lids

Several handfuls Total® cereal

Medium-sized bowl

Pestle or heavy spoon

Several handfuls dirt

Elements of magnetic money, rocks, beach sand, Total® cereal, and dirt

Fold the $1 bill tightly into a roughly ½-inch square and hold it together with cellophane tape, as shown. Show that the $1 bill is attracted to the strong magnet.

Magnetic money

Next, show that the rock can be suspended under the magnet. You will need to find a suitable rock before you begin—not all rocks are attracted to a strong magnet. Go to a beach or a streambed or anywhere where there is a large variety of rocks, touch your strong magnet to different small stones, and in a short time you should be able to find one that will work for this demonstration.

Magnetic rock

Place a large handful of beach sand in one of the jars and secure the lid. Turn the jar upside down and tape the magnet to its bottom. Shake the jar briskly for a few minutes, then remove the lid and slowly pour out the sand. A tablespoon or so of coarse, strongly magnetic black powder will remain in the jar, attracted to the magnet.

Magnetic beach sand

Remove the magnet from the jar and pour the black powder into another small jar for safekeeping. Using the same sand, repeat the procedure a few times to separate a bit more magnetic material from the sand. Transfer the black magnetic powder to the other small jar and set aside.

Using additional handfuls of sand, repeat the process, transferring the black magnetic powder that’s collected to the second jar as you go. (This powder can be used to make a crude but effective Magnetic Mountain demonstration, which is described in Experiment 7.)

Place a large handful of cereal in the bowl and, using the pestle or spoon, grind it into a very fine powder. Pour the powdered cereal into one of the jars and secure the lid. Turn the jar upside down, tape the magnet to the bottom of the jar, and briskly shake the jar for a few minutes. Remove the lid and slowly pour out the powdered cereal. About a teaspoon of magnetic material will remain inside, attracted to the magnet. You may have to repeat this process a few times, using new bowls of cereal, to collect a significant amount of magnetic material. Shown on page 4 is a small amount of magnetic cereal matter suspended in a plastic bag.

Magnetic Total® cereal

Finally, take a few handfuls of ordinary dirt from the garden and refine it in the same manner as for sand. This photo shows the jar of magnetic dirt suspended below the magnet.

Magnetic dirt

The Science Behind It

Why are all these things magnetic?

In each case, the black magnetic material that’s collected is iron oxide. Iron is the fourth most abundant element in the earth’s crust. The most abundant iron oxide is black Fe₃O₄, which is strongly magnetic. A $1 bill is magnetic because the black ink on the portrait side of the bill is loaded with black iron oxide Fe₃O₄ pigment. The bill contains only about 5 mg of the oxide. The bill weighs almost exactly 1 gm, so the Fe₃O₄ present in the pigment is easily holding up more than 200 times its own weight! This Fe3O4 pigment was originally put in the ink to make it black, not to make it magnetic. The hysteresis loop of a $1 bill is shown below. The coercivity is about 100 Oe and the remanent moment is appreciable.

Hysteresis loop of a $1 bill

The image on the next page was made by scanning the surface of a $1 bill with a magnetic read head similar to those used in modern tape recorders and hard disk drives. (The image is courtesy of Fred Chamberlain, who was at San Diego Magnetics at the time that he provided it.)

Magnetic image of a $1 bill

Comparing the magnetic image above to an actual dollar bill, the observant viewer will note that the treasury seal on the left side of the portrait is black, but is not magnetic. That is because the black ink in the seal contains no Fe₃O₄. This fact is the basis of some simple counterfeit currency detectors.

The rock shown in this experiment is magnetic because it also contains Fe₃O₄. About 1 in 20 Southern California beach rocks is slightly magnetic, while about 1 in 100 rocks is magnetic enough to be picked up.

Below is an M-H loop of the powdered cereal. Also shown is an almost identical loop of metallic iron powder.

M-H loops of Total® cereal and iron powder

The obvious conclusion from this plot is that Total® fortified cereal is “fortified” with iron that has been added in the form of metallic iron powder. It remains to be seen if metallic iron is digested and absorbed by the body.

The beach sand and dirt both contain varying amounts of Fe₃O₄. The rock, sand, and dirt all have M-H loops very similar to that of the $1 bill, because all three contain small particles of Fe₃O₄.

Experiment 2

The Super Strong Magnetic Nail

A common nail is used to pull a string of small steel objects off a very strong magnet. The objects remain suspended under the nail until the magnet is removed, whereupon they fall off.

Materials

8-cm long iron framing nail

3 common steel balls measuring 1.3 cm, 1 cm, and 0.8 cm, respectively

1-cm square steel nut

Very strong 5-cm by 5-cm by 2.3-cm NdFeB magnet (magnetized in the 2.3-cm direction)

Super strong nail equipment

A nail alone...

Table of contents

• Cover
• Title
• Copyright
• Contents
• Introduction
• 1 Magnetic Money, Rocks, Beach Sand, Total® Cereal, and Dirt
• 2 The Super Strong Magnetic Nail
• 3 The Magic Table Knives
• 4 The Mysterious Magnetic Arch
• 5 The Strange “Zinging” Magnets
• 6 The Amazing Magnets That Fall Through Each Other
• 7 The Magic Magnetic Mountain
• 8 The Magnetic” Hedgehog”
• 9 Mercurial Water
• 10 The Magnetic Jumping Jack
• 11 The Nail That Standson Its Point and One That Won’t
• 12 The lnvisible Magnetic Bowl
• 13 Why the Magnet Stays in the Hole
• 14 The Washers and the Coat Hanger
• 15 The Strange, Reversing Magnetic Field
• 16 The Compass That Points Only North or South
• 17 The Mysterious Compass That Changes Its Mind
• 18 The Floating Globe
• 19 The Super Levitron® Floating Top
• 20 The Floating Magnet
• 21 The Floating Sheet of Carbon
• 22 The Rolling Disk
• 23 The Red Sea Effect
• 24 Invisible Magnetic “Syrup”
• 25 A Magnetostatic Linear Accelerator
• 26 The One-Candle-Powered Pendulum
• 27 The Amazing Lengthening (or Shortening) Magnetic Materials
• 28 The Crazy Spinning Balls
• 29 The Spinning Ball That Rolls East or West, but Not North or South
• 30 The Popping Magnet
• 31 The Rolling Magnets
• 32 The Little Motor That Shouldn’t Run, but D oes Anyway
• 33 The Magnetic Picture Sheet
• 34 The Strange Magnetic Physics Taking Place on Your Refrigerator
• 35 Magnetic Recording Made Visible
• 36 The Amazing Magnetic Hot Glue
• 37 The Magnetic Patterns That Cant Be Erased
• 38 The Sliding Magnet
• 39 Magnetic Bacteria
• 40 The Earth as a Magnetic Recorder
• About the Author
• Index