40 AT T RACTI V E
( AND REPULSI V E )
DE VICES & DEMONSTRATIONS
Contents
Introduction v
1 Magnetic Money, Rocks, Beach Sand, Total® Cereal,
and Dirt 1
2 The Super Strong Magnetic Nail 9
3 The Magic Table Knives 13
4 The Mysterious Magnetic Arch 17
5 The Strange “Zinging” Magnets 21
6 The Amazing Magnets That Fall Through Each Other 23
7 The Magic Magnetic Mountain 27
8 The Magnetic “Hedgehog” 31
9 Mercurial Water 35
10 The Magnetic Jumping Jack 37
11 The Nail That Stands on Its Point and One That Won’t 41
12 The Invisible Magnetic Bowl 45
13 Why the Magnet Stays in the Hole 49
14 The Washers and the Coat Hanger 51
15 The Strange, Reversing Magnetic Field 53
16 The Compass That Points Only North or South 59
17 The Mysterious Compass That Changes Its Mind 61
18 The Floating Globe 65
19 The Super Levitron® Floating Top 67
20 The Floating Magnet 69
21 The Floating Sheet of Carbon 75
22 The Rolling Disk 77
23 The Red Sea Effect 81
24 Invisible Magnetic “Syrup” 83
25 A Magnetostatic Linear Accelerator 87
26 The One-Candle-Powered Pendulum 91
27 The Amazing Lengthening (or Shortening) Magnetic
Materials 95
28 The Crazy Spinning Balls 99
29 The Spinning Ball That Rolls East or West, but Not North or
South 101
30 The Popping Magnet 103
31 The Rolling Magnets 107
32 The Little Motor That Shouldn’t Run, but Does Anyway 111
33 The Magnetic Picture Sheet 115
34 The Strange Magnetic Physics Taking Place on Your
Refrigerator 121
35 Magnetic Recording Made Visible 123
36 The Amazing Magnetic Hot Glue 127
37 The Magnetic Patterns That Can’t Be Erased 131
38 The Sliding Magnet 137
39 Magnetic Bacteria 141
40 The Earth as a Magnetic Recorder 145
About the Author 149
Index 151
Magnetic Money, Rocks, Beach Sand, Total® Cereal, and Dirt 1
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
2 Mondo Magnets
Fold the $1 bill tightly into a roughly 1⁄2-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 dif-
ferent small stones, and in a short time you should be able to find one
that will work for this demonstration.
Magnetic rock
Magnetic Money, Rocks, Beach Sand, Total® Cereal, and Dirt 3
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 pow-
der 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 proce-
dure 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 Moun-
tain 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 tea-
spoon 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.
4 Mondo Magnets
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
Magnetic Money, Rocks, Beach Sand, Total® Cereal, and Dirt 5
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.
B: 1 inch = 2.500E-01 Mx
H: 1 inch = 2.500E+02 Oe
Hm = 1005 Oe
Hc = 104 Oe
Data ID—Frn Loop Ph1-m = 0.504 Mx
Temp = 23.0 Deg. C Ph1-r = 9.842E-02 Mx
Data Accepted SR = 0.20
KR = 0.518
LDJ Incorporate Delta – H = 639
Model 7500A BH Meter SFD = 6.06
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 Chamber-
lain, who was at San Diego Magnetics at the time that he provided it.)