High School Mathematics-Physics SMILE Meeting 1997-2006 Academic Years Magnets

30 September 1997: Alex Junievicz [CPS Substitute Teacher]
did a demonstration involving a "cow magnet" [used by farmers to remove metallic objects from cow stomachs] dropped down tubes that had inside diameters a little larger than the diameter of the [roughly cylindrical] magnet. He showed that the magnet fell quite freely inside a plastic [PVC] pipe, whereas for a copper pipe it was slowed down [presumably by eddy currents], even though the copper pipe had a longitudinal strip removed from it. Alex was very surprised that, when he cut the tubing lengthwise, there was little change.  He expected breaking the short winding that there would be little effect on the magnet. There was less Cu, and perhaps that was the main reason for the faster travel.

The magnet fell quite freely through an aluminum pipe of somewhat larger diameter, however. The Al pipe [scrounged from the shop by Lee Slick] was very short and thin, and the eddy currents may not have been set up well in it. The definitive experiment would require a solid copper pipe, and an Al pipe with thick walls.

Cow magnets are not digested when in cows [four] stomachs, but they do catch metal objects, filings, barbed wire, etc in the 1st Stomach of a cow preventing damage further on. The magnet, which  I got from Farm and Fleet in Wisconsin, has 5 smaller magnets and is about 3 cm long and about 1/2 inch diameter. Thus tubing with a 1/2 inch ID will work. I used a 4 ft piece of pipe (\$4.20 for the Cu and \$1.40 for 10 ft of PVC conduit; the cow magnets were approximately \$2 each in packets of 3)

14 October 1997: Alex Junievicz [CPS substitute teacher]
brought in an Al tube cannibalized from a TV antenna.  Although it has several holes from the previous life a cow Magnet slid slower than the PVC pipe, but still quite fast. He acquired another Cu pipe without a slit and the magnets went slower in the Cu pipe with a slit down the tube which was shorter. During the ISPP meeting the tubes were "massed". The slit tube was 649 g and the complete tube was 551 g. Both tubes were purchased in the Plumbing Department. Farm and Fleet in Kenosha WI was the source of the Magnets and the one that now has a slit and Home Depot [Route 59 and 75th Street] was the source of the one still complete. I assumed that both were for plumbing and have the same thickness. Still what is surprising is that the slit seems to make no difference.

08 September 1998: Bill Blunk [Joliet Central HS]

Knob Magnets available at All Electronics Corporation
http://www.allelectronics.com/
Part # Mag 32 1-800-826-5432
\$3.00 each + \$5.00 charge per order.
Al Coins available at WTTW Store of Knowledge

He demonstrated that the fall of an Aluminum "coin" was greatly slowed when dropped between 2 of these assemblies cascaded. The second assembly greatly slowed it down.

He suggested that 2 in parallel produced a longer field region, because of addition of the fringing fields.

29 September 1998:  Earl Zwicker [IIT retired]
He dropped an Iron plate with a magnet just above it.

```He showed it this way:
| ---------   |
|  Magnet   |
|           |
|  Fe plate |
__________
```

When the assembly dropped the plate resting on the bottom comes up to the magnet but before they stay separated.

13 October 1998: Larry Alofs [Kenwood HS]
He talked about cow magnets [obtained from the farm store in Kewaunee] and sold them for \$2.50 each. They have a variety of uses, including those on the farm.

** Magnets ***

20 April 1999: Larry Alofs [Kenwood High School]
Space Pendulum revisited.
He tried to explain some of seemingly perpetual (SP) devices that have rotating magnets that are activated by electronics

The coils are loosely wrapped around an iron rod so that they can be slid on and off so that the correct orientation of the coil can be determined by trial and error. The PVC pipe is hung so that it can swing with the cow magnet about 0.5cm above the top of the coil. The 12V auto tail light bulb is the circuit to protect the transistor in case something goes wrong.

26 October 1999: Larry Alofs (Kenwood HS)
had showed us "action at a distance" very real graphic. A small board (maybe 12 in long) had a clothes pin fixed at one end, and a vertical board (about 7 in) at the other end, with a cow magnet held on top. A piece of string had a paper clip tied to one end, and the other end was held by the clothes pin. The paper clip was held near the magnet, and the length of the string adjusted (using the clothes pin as a clamp) so that the attractive force between magnet and paper clip held the string stretched out toward the magnet, with no visible means of support. Striking! One could study effectiveness of the magnetic shielding of various materials using this. Larry had cow magnets for sale at cost, about \$2.50 each. Beautiful!

11 April 2000: Arlyn Van Ek (Iliana Christian HS)
somewhat randomly handed out Genecons to us. (See the Arbor Scientific Catalog, or the website http://www.arborsci.com)

Cranking Up: physics lab

Each Genecon is a fist-sized, roughly ellipically-shaped plastic generator/motor with a crank sticking out of one end and a pair of wires from the other end; see http://www.arborsci.com/detail.aspx?ID=543. Arlyn had the wires connected to a small light bulb mounted in a socket. When he turned the crank, the bulb lit up. When he opened the connection to the bulb and cranked again, he said it felt different, and invited those of us with Genecons to check this out. Sure enough! We could see the our friends break into smiles! Then others tried it. It was much harder (took more work) to crank with the bulb in the circuit and lighting up, than out of the circuit and remaining dark. A beautiful way to show students just how much (electrochemical) work a battery is doing when it is lighting a bulb!

Next, Arlyn connected three bulbs in series with each other and an ammeter, then turned the crank hard and fast as he could to light the bulbs. We read 0.3 amperes. He repeated this with the same three bulbs in parallel, and we read 0.9 amperes. More current! (Think about it!)

Finally, he connected his Genecon to a small capacitor and cranked, charging the capacitor. He noted that as the capacitor became charged, it took less effort to turn the crank. When he released the crank, somewhat to our amazement, the crank continued to turn by itself! -- and even more interesting -- in the same direction as Arlyn had been cranking it! "How come??" Arlyn wanted to know. How do we explain this? John Bozovsky and Camille Gales connected their two Genecons together, and when John cranked his, the handle on Camille's rotated! Ahah! The Genecon being cranked by John was converting mechanical energy to electrical. The electrical energy was fed to Camille's Genecon which acted as a motor so that its handle then turned. Neat! When John reversed the direction of his cranking, the motion of the handle on Camille's Genecon reversed itself. When we thought about it, we saw this should be an expected symmetry in behavior between the two Genecons, and it was pleasing to see. Wonderful physics, Arlyn! Thanks!

05 September 2000 Bill Blunk (Joliet Central HS)
showed us the Orbitron magnetic toy. (Manufactured by Binary Arts, and available at the website of The Parents-Choice organization: http://www.parents-choice.org/product.cfm?product_id=1839&award=xx&from=ThinkFun. Essentially, it was made with two chrome-plated heavy wire rings, of equal diameter (about 27 cm), held coaxially a fixed distance apart (by a frame of some sort). A small but massive metal top had magnetized axles, which held it onto the pair of rings.

If the rings were held with axis horizontal, and the top place at rest at the highest position, the top would gradually start spinning as it moved down and around the pair of rings until it reach the bottom, then continued on up the other "side" - but not all the way. Some energy had been lost. Bill told us how he tried to increase the speed of the top to reach the point at which the magnetic force keeping it in contact with the rings would no longer supply sufficient centripetal force to keep the top moving in a circle, so it would then "fly off" -- but there were problems.

Next, Bill showed us another toy (Lumberjack Toys,7651 Herrington NE Belmont, MI 49306) which used a tethered ball one could project up toward a small basketball hoop, and try to make a "basket." Shows transition of kinetic energy into gravitational potential energy, as well as being fun. The toy is available at the following location:

Amazing Toys
319 Central Avenue
Great Falls MT 59401
(406) 727-5557 [Bob Pechlin]
http://www.amazingtoys.net

Thanks, Bill!

12 September 2000 Larry Alofs (Kenwood HS)
made a simple pendulum by attaching a string to the ceiling and suspending a small plastic bag (containing small pellets) tied to its bottom end so it hung about 10 cm above the table top. He reminded us that ferromagnetism gives rise to the strong attractive and repulsive forces that most of us associate with magnetism and permanent magnets. But then he told us about diamagnetism, which gives rise to forces about 100,000 times weaker than ferromagnetism. And the force is always repulsive! Larry explained that the pellets in the plastic bag were made of Bismuth (Bi), which is diamagnetic. Could we detect this very small force? -- Larry wondered. He held up a very strong neodymium magnet and asked, "Is there repulsion of the Bi from this magnet?" He then moved the magnet close to the Bi pellets and then away, repeatedly using any very weak repulsive force to push the pendulum into motion. Sure enough! By pushing with the resonant frequency of the pendulum, we could see that Larry had set it swinging so it moved back and forth in an arc of about 0.75 cm! Marvelous! Larry showed us something very few people ever see and even realize exists: the repulsive force associated with diamagnetism. A real phenomenological approach! Thanks, Larry!

26 September 2000 Larry Alofs (Kenwood HS)
held up a transparent plastic gadget called Mysterious Magnet Tube, from Science Kit ; telephone number 1 (800) 828-7777; website http://www.sciencekit.com (cat.no.46213, \$12.95). Imagine a cylinder about 9-10 cm in diameter and 10 cm long with its open ends sealed off. Then place a smaller diameter (say 1.5 cm) cylinder coaxially with it, which pierces through the sealed ends of the larger one. In the space between the two are some iron filings. When Larry placed a cow magnet into the smaller cylinder which then could travel within the larger one, the iron filings lined up to trace out the shape of the 3-D magnetic field surrounding the cow magnet! Neat! We recalled the "poor man's" version made by Harry Hasegawa (ret- Lawndale Comm.Acad.) from a transparent soda bottle, a plastic tube, iron filings and some epoxy putty to seal it. Larry passed it around for us to play with. Thanks, Larry!

24 October 2000 Larry Alofs (Kenwood HS)
made a presentation titled: Repulsive Fruit. He had fashioned out of copper wire (no.12?) and an inverted beaker a kind of balance. The wire behaved like a teeter totter, about 16 inches long, and supported at its center by the sharp point of one of its ends resting on the glass of the inverted beaker; this formed a low friction bearing. (The wire drooped down from the center toward both ends, giving it stability, with its center of gravity below the point of support.) While the wire was free to move up and down vertically, it was also free to rotate in a horizontal plane about the vertical axis through its point of support on the beaker.

Next, Larry took a grape from a cluster of grapes he had bought at a store. He stuck the grape onto one end of the wire teeter totter. The entire affair balanced about that central support point. Larry then took a small but very powerful, rare-earth magnet, and moved it carefully to within a millimeter or two of the grape. Any force acting between the magnet and the grape would result in rotation of the wire. The grape (and the wire) very slowly began to move away from the magnet, rotating in a circular path. Larry moved the magnet so that it continued to stay within a millimeter or so of the grape. Soon the wire teeter-totter-with-grape was obviously rotating in a circle, and it was clear that the magnet must have exerted a small repulsive force on the grape! To help convince us, Larry repeated the experiment, but this time to produce rotation in the opposite direction. Larry told us that a piece of apple worked also, and a rubber stopper worked, but with a noticeably weaker repulsive force. A glass marble, taped to the end of the wire, worked better than the rubber stopper, but not as good as the grape. The repulsive force is believed due to diamagnetism associated with the water molecules in fruit. See snacks on the Exploratorium Museum [San Francisco] website, and particularly the webpage http://www.exploratorium.edu/snacks/diamagnetism_www/index.htmlLarry gave us copies of that page.

He also drew a diagram on the board showing two horizontal slabs of bismuth (a diamagnetic material) separated by a small distance. An electromagnet placed above the upper slab produces a magnetic field in the space between the slabs, and a small but strong, permanent magnet may then be made to "float" when placed in the space between the slabs.

What a beautiful way to show diamagnetism in action! Thanks, Larry!

24 October 2000 Porter Johnson (IIT Physics)
gave us some insight into paramagnetism (materials with unpaired electrons). Such materials are weakly attracted to both poles of a magnet. Diamagnetic materials are weakly repelled by both poles of a magnet. Bringing a magnetic pole near creates electron orbital currents in such a direction as to set up an opposing magnetic field (Lenz's Law), producing repulsion. In ferromagnetic materials such as iron, cobalt, nickel, the magnetic fields of spinning electrons in the atoms become completely lined up within small regions called domains. Each domain is completely magnetized. But the domain directions of magnetization tend to be random, and their magnetic fields average out to zero in the material. However, if the material is placed in an external magnetic field, the domains re-orient so their directions of magnetization line up, resulting in very strong magnetism of the material. They then hold themselves in alignment after the external field is withdrawn, because of the strong internal and external field they produce. It is not until the temperature is raised to a certain point (the Curie Temperature) that the thermal motion of the atoms destroys the magnetic alignment within domains, and the strong magnetism disappears.

05 December 2000 Larry Alofs (Kenwood HS)
showed us the Curie point in action! He held up a 1979 Canadian quarter which has a high nickel content, and is therefore ferromagnetic. He tied the quarter to the end of a piece of copper wire, using the wire itself to tie with. This formed a kind of pendulum with the quarter serving as the bob at the bottom end. Holding on to the top end of this pendulum, he brought a magnet near the quarter; the quarter was attracted toward it, and swung closer so that the wire made an angle to the vertical. Aha! Now we knew that the quarter is indeed ferromagnetic! Next, Larry suspended the wire-and-quarter pendulum from the end of a horizontal rod held by a ring stand. He fixed the magnet to a clamp on another ring stand and moved it closer to the quarter so that the wire-and-quarter pendulum again swung out and remained at an angle to the vertical. He now lighted an alcohol burner and placed it so that its flame enveloped the quarter from below. After perhaps ten seconds, the pendulum suddenly swung downward toward its ordinary (vertical) equilibrium position. The attractive force between the quarter and the magnet had suddenly disappeared! But after several more seconds, the pendulum swung out at an angle and remained there so that the quarter was again enveloped by flame. The attractive force had suddenly reappeared! And then the whole cycle repeated itself, over and over! Remarkable!

Larry explained that ferromagnetic materials such as iron and nickel are made up of tiny domains (perhaps 0.001 cm or 10 microns in diameter) which are completely magnetized. When the material is placed in a strong magnetic field, the domains become aligned so their directions of magnetization are the same, and the entire material becomes a strong magnet. However, when heated to a sufficiently high temperature, the thermal motion becomes so great that the domains vibrate out of magnetic alignment and become randomly oriented, and the material loses its magnetic behavior. The temperature at which this occurs is called the Curie Temperature, and it is different for each ferromagnetic material. For Nickel it is 358 oC, whereas for Iron it is much higher; 770 oC, At temperatures below the Curie point, domains may again become magnetically aligned and the ferromagnetic properties of the material are restored. Beautiful! Thanks, Larry

01 May 2001 Bill Blunk (Joliet Central HS, Physics) (A Harald Jensen Presentation)
showed us a ceramic disk magnet (magnetic particles imbedded in ceramic material) that had a hole through its center, for which the front surface was the North Pole of the magnet.

• Question:  Why does a magnet pick up a paper clip?
• Answer:  Because the magnet induces magnetism in the paper clip, turning it into a magnet but with opposing polarity, resulting in attraction.
• Question: Why does the paper clip become a magnet?
• Answer: Because it is made of a ferromagnetic material, iron. And the iron is made up of microscopic crystals or grains called domains which are as fully magnetized as they can be. But the domains are randomly oriented throughout the unmagnetized iron, so the overall magnetism of the paper clip averages out to zero. But when a magnet is brought near the paper clip, the domains become aligned in its field, and their magnetism no longer averages out to zero, resulting in the attraction to the magnet.
• Question: What causes ferromagnetic domains?
• Answer: Bill connected a small coil of wire to a battery so a current flowed, and brought it near a compass needle. Knowing the polarity of the battery and predicting (with the right hand rule) the direction of the magnetic field associated with current loops of the coil, we saw that the compass needle was repelled, confirming the correctness of the prediction. Bill said that the ferromagnetic domains may be thought of as tiny current loops within the material. When their magnetic directions are lined up by the field of an external magnet, the material becomes magnetized.

Bill sketched the ceramic disk magnet on the board, with its north pole facing us, and sketched many current loops (representing the domains) and showing the current in each loop as counterclockwise, consistent with the face of the ceramic magnet being a north pole. With each loop drawn next to its neighbor, it was easy to see that their currents would would cancel out, except at the outside circumferential surface on the rim of the magnet, where the loops had no neighboring current loop for cancellation. Thus, there is a surface current I counter-clockwise as seen from the front, and a surface current -I (clockwise as seen from the front) would circulate around the inner hole.

Bill demonstrated the presence of the outer current loop by placing a small compass needle attached to a non-magnetic brass shaft hear the outer edge of the magnet, and showed that the field points outward.  Then, he placed the same needle near the inner edge, and showed that the field pointed in the opposite direction--inward.  Thus, the presence of the surface currents are detectable.  Very nice, Bill!

Of course, that is not the end of the questions one may ask. Why can we think of the domains as tiny current loops?  But we'll leave that for another day! (The answer lies with unpaired electron spins within the domains.)

You did Harald Jensen proud, Bill!

04 December 2001: Leticia Rodriguez (Ruben Salazar Bilingual Center) Experiment with Magnets, Continued
We divided into teams of two and performed an experiment using disc-shaped, pressed ceramic magnets and paper clips.  On a flat horizontal table, we brought the magnet and the paper clip [which lay directly away from the magnet] closer together, until the paper clip jumped over to the magnet.  Then each group recorded the distance of separation (jump distance) between the paper clip and the magnet at which the jump occurred. The experiment was repeated with 2, 3, and 4 magnets stacked on top of one another and one paper clip. The measurements were distributed in the following way.

 Magnets and Paper Clip Number of Magnets Distance (mm) 1 3- 5 2 6 - 9 3 10 - 13 4 12 - 15

We drew a graph of the jump distance versus the number of paper clips, which showed that with more magnets, the separation distance increases. We also experimented with the magnets as we moved them closer to one another. Do they attract or repel? This is a simple yet very interesting exercise in magnetism. Good work, Leticia!

25 March 2003: Arlyn van Ek [Illiana Christian HS, Physics]      Magnetic Fluids
Arlyn
show us a Magnetic Fluid [Chemical Demonstration Kit, Catalog Number AP4681 about \$20], which he had recently obtained from Flinn Scientific Inchttp://flinnsci.com/.  The material is a liquid that is pushed to move easily between two transparent cylinders by plungers, until a small magnet is brought close to the narrow tube joining the cylinders.  The fluid quickly "freezes", and cannot be pushed. Here is some information provided with the apparatus:

"The material in this fluid device is a Magneto-Rheological Fluid, or MR Fluid.  MR fluid is a suspension of micronized, magnetically susceptible (iron/steel) particles in water with suspension additives.  Under normal conditions, MR fluid is a free-flowing liquid with a consistency similar to that of very thick motor oil.  Thus, the fluid can flow freely between the syringes under pressure from your hand on the piston.  Exposure to a magnetic field, however, can transform the magnetically susceptible particles into a near-solid mass in just milliseconds.  The solid forms when the particles in the fluid align with the magnetic field lines of the magnet.  The space between the particles is diminished and the fluid cannot flow, taking on the properties of a solid mass.  The fluid can be returned to its liquid state with the removal of the magnetic field."

These magnets don't really "go with the flow", Arlyn!  Fascinating!

08 April 2003: Michelle Gattuso [Carl Sandberg HS Orland Park, Physics]        Seeing Things with Bar Magnets
Michelle
showed us how to see the fields produced by magnets, using an overhead projector, along with the (transparent) Magnetic Field Observation Box, which is available from Arbor Scientific [http://www.arborsci.com/detail.aspx?ID=662]. The following information is excerpted from that webpage:

Forget the mess of iron filings and the constraints of two-dimensional representations of magnetic fields - this self-contained device reveals the proper, three-dimensional nature of magnetic lines of force. The sealed acrylic box contains iron filings suspended in a silicone oil solution. A cylindrical magnet (included) is dropped into a central chamber to create the three-dimensional field. Other magnets can be applied to the sides or ends of the box to demonstrate interesting interactions between fields. Although primarily designed for individual study, the observation box can also be placed on an overhead projector for a two-dimensional demonstration of the field (4" x 2" x 2")
Activities and uses:  Use the Magnetic Field Observation Box to study magnetic fields in three dimensions. Look at the field from a single provided magnet or bring iron or another magnet near and see the results.  Bring another magnet close to the box and insert the bar magnet in the hole.  The iron powder is magnetized in two areas showing attraction and repulsion of magnetic forces.

Michelle inserted a magnet into the hole in the box, and we saw the field lines very nicely on the overhead projector.  She placed two magnets into the hole with like poles adjacent, and later with unlike poles adjacent.  It was quite easy to see the difference in these cases, with the field lines seeming to push the magnets apart in the first case, and to pull them together in the second case.

The projector is a godsend for this demo! Way Cool, Michelle!

23 March 2004: Ann Brandon  [Joliet West, Physics]           Current without Batteries??
Ann began by outlining the approach she took in teaching magnetism in 6 class periods, according to the following plan:

1. Day 1: She placed a permanent magnet under a sheet of paper, and placed small compasses on top of the paper.  The compasses pointed in the direction of the magnetic field at their locations, and thus she could indicate the pattern of magnetic fields surrounding the magnet.  Then, she sprinkled iron filings onto the paper.  The filings also indicated the direction of the magnetic field, by forming a pattern that revealed the lines of force.
2. Day 2: She borrowed a plastic funnel with a long stem from the Chemistry laboratory, and turned it upside down on the table.  Then she put ring magnets onto the stem, with adjacent poles repelling one another.  She measured the distances between the magnets.  Then she determined the downward force on each magnet, since a given magnet would have to support the weight of all magnets above it. The students drew a graph of the force F versus the separation D between magnets.  They obtained an inverse square law F = K / D2.  But, why??
3. Day 3: Build an electromagnet and hold up 10 paper clips with it, using wire, a nail, and a battery.
4. Day 4: Build a Rudy Keil electric motor using a battery and magnet
5. Day 5: Summary; review; example problems.
6. Day 6: Producing Current in a Coil of Wire (Look Ma! No Batteries!)
Materials:
2 small coils of wire (Gilley Coils), galvanometer (micro-Ammeter), 2 different bar magnets, large coil of wire (air core solenoid).
Procedure:
Label one end of each magnet as North. Connect the galvanometer to one of the small coils.
Move the N pole of one of the magnets through the center of the coil. What happens to the galvanometer needle?
Pull the magnet back out of the coil.  What happens to the needle now?
Try the South Pole this time.  What happens to the needle this time?
Instead of moving the magnet, move the coil.  What happens to the needle?
What seems to be required to produce current?
Try the other magnet.  What differences do you observe?
Move the best magnet in and out faster than before.  What differences do you observe?
Connect the large coil to the galvanometer.
Try dropping the best magnet through the large coil.  CATCH THE MAGNET!  What difference did this make?
If the bar magnets were replaced by an electromagnet, how could you increase the current through the galvanometer?
Conclusion:  Which things affect the current in the galvanometer?
If you have time, connect two small coils together in series with the galvanometer.  Place the two coils so that their center holes line up.
Move your best magnet into the center of the two coils.  Pull it out fast.  What happens to the galvanometer?
Turn one of the coils around (180°).  Place the best magnet into the center of the two coils.  Pull it out fast. What happens to the galvanometer this time?
Why should you have different results?

Beautiful phenomenological physics, Ann!

20 April 2004: Marilynn Stone and Don Kanner  [Lane Tech HS, Physics]         Dropping Weights through Pipes
Marilynn
took a brass weight, and held a copper pipe [about 2.5 cm in diameter and 1.5 meters long] vertically with the bottom just above the floor.  She dropped the brass weight through the pipe, and it hit the floor less than 1 second later, according to our estimates.  Then she dropped a strong magnet of about the same size through the pipe, and it took an estimated 8 seconds to hit the floor.  How come?  The slow-down was caused by eddy currents set up in the pipe by the moving magnet, which produced an upward force on the magnet.  She passed the magnet and pipe around the room, and we each looked down the pipe with fascination as the magnet slowly drifted down the pipe.  Don Kanner then asked whether the size and material constitution of the pipe made any difference in the motion. He dropped the weight through a slightly larger copper pipe, and we noticed that it got to the ground more quickly. He also dropped a cow magnet through the same pipe -- the cow magnet fell more quickly, because it produced a weaker field (in proportion to its weight) than the original magnet.  What about putting the smaller pipe concentrically inside the larger pipe?  We observed that the original magnet took longer to fall through the two pipe system, in comparison with falling through only one of the pipes.  Why?  The eddy currents induced in each pipe produced a stronger upward force on the magnet.  We next took these measurements for the various cases:

 Case Time for Fall Brass weight inside (2.5 cm) Cu pipe 0.58 sec Cow Magnet inside (2.5cm) Cu pipe 0.6 sec Cow Magnet inside concentric Cu pipes 1.7 sec Strong magnet inside 4 cm Al pipe 3.0 sec Strong magnet inside 2.5 cm Cu pipe 7.7 sec Strong magnet inside concentric Cu pipes 11.3 sec

A "pipe drop" was preformed by the late Alex Juniewicz at the SMILE meeting of 30 September 1997.

Bill Blunk took an aluminum parking token [valid in parking meters throughout the mighty metropolis of Great Falls, Montana], and dropped it through the gap between the two small magnets. The token passed slowly through the field region, and then fell tot he floor.  Interesting!  For more details see the writeup of the the SMILE meeting of 08 September 1998.

Thanks for "dropping in", Marilynn and Don!

12 October 2004: Bill Blunk [Joliet Central HS, recently retired]           Finding Metallic Stakes to Mark Property Lines
Bill  was seeking to find the location of iron stakes driven into the ground to mark the edges of his property line.  Some of the white plastic caps on the stakes had disappeared, and the stakes themselves had presumably been pushed into the ground, and were no longer visible.  How could he find the (underground) stakes to establish the property lines?  A surveyor suggested using a metal detector, but Bill didn't have one.  [See the website How Metal Detectors Work:  http://home.howstuffworks.com/metal-detector1.htm.] Instead, he took out his trusty Boy Scout compass, and began to paw around in the ground in the probable location of one of the stakes.  Bill reasoned that the stakes would have been magnetized slightly as they were being driven into the ground.  He scanned over a 4 meter ´ 4 meter region. He found that the compass generally pointed in the direction of the earth's magnetic field --- 15 degrees East of North and at an inclination of about 60 degrees below the vertical, for this location in Montana.  However, in one small region the compass deviated from this direction, when the needle was free to rotate in the horizontal plane, as well as in a vertical plane.  He dug down at that location, and found the stake, about 10 cm below the surface.  In a similar fashion he found another boundary marker.  Using the survey map, he readily found the approximate location of the other markers. Two of them in relatively remote locations were above the ground, with the white plastic cap still present.  Good physics makes up for the lack of equipment, once again!  Very impressive, Bill.

Porter Johnson indicated that the Northwest Territory, consisting of the present states of Ohio, Indiana, Michigan, Illinois, and Wisconsin, was well-surveyed, and laid out into townships, sections, and plots, under the Articles of Confederation in the 1780's.  This tradition of careful layout of the land was generally followed for land settled in the West.  However, such a systematic layout has never been done in the Northeast, or in the South.  The street pattern of the city of Boston was laid out along old cattle trails -- but it has remained a mystery as to why the old trails were so crooked!  In the middle Atlantic states there is an elaborate network of boroughs completely surrounded by independent townships.  Throughout the Appalachian regions,  property boundaries were often set by the lay of the land, boundaries being determined by banks of streams and  rivers, crests of hills, big trees, and the like.  In that region the property lines are frequently in dispute to this day, even in populated areas.  The subject of geometry (earth measure) was invented by the Greeks and Egyptians living in the Nile Delta to re-establish property lines after the annual flooding of the river.

Bill next took some strips of Mu-metal (permalloy), which is often used for magnetic shielding [http://www.fact-index.com/m/mu/mu_metal.html].  When held in a direction along an external magnetic field B, these strips become slightly magnetic, because of an induced internal field.  To test this assertion, he took two of these strips, and held them in a North-South direction at an inclination of about 45 degrees below the horizontal.  He showed that opposite ends of the strips would attract one another weakly, as an indication that the fields induced in the strips were in the same direction.  It was important to keep the strips in the proper orientation (parallel to the earth's field) while showing this attraction, since the effect quickly disappears when that orientation is changed.

26 October 2004: Wanda Pitts [Vernon Community Academy]                   Magnets (handout)
Wanda
passed around the article Attractive Spirals from the book Janice VanCleave's Magnets: Mind-boggling Experiments You Can Turn Into Science Fair Projectshttp://www.amazon.com/Janice-VanCleaves-Magnets-Mind-boggling-Experiments/dp/0471571067
She began by asking us what we know about magnets. We came up with the following:

• they have North and South poles
• things containing iron stick to them
Then she asked us about electromagnets and gave us materials to make an electromagnet, which we then proceeded to do. Ron's magnet, with two layers of densely wound coils of wire, picked up seven BBs!

Ken pointed out that one may wrap aluminum foil around the nail  in making an electromagnet. It does not short out against the nail because the foil is coated with a non-conducting coat of aluminum oxide  Al203 (i.e., the foil surface is naturally insulating).

Other connections between magnets and biology /chemistry:  MRI imaging, helping birds migrate (by following the magnetic field of the Earth).

07 December 2004: Leticia Rodriguez [Peck Elementary School]           Magnetic Fishing Pole
Leticia tied one end of a string to the end of a wooden stick, and attached a small magnet to the other end.  Holding the stick, she showed how this fishing pole could be used to test materials for magnetization.  Some materials (aluminum keys, US quarters, plastic spoons, etc) are not attracted to the magnet, whereas others (steel keys, old Canadian quarters, chewing gum wrappers, etc) are attracted to it.  Students made two lists:  Magnetic Objects and Nonmagnetic Objects.  This was a very good introduction to scientific observation and "experiencing science".  Thanks, Leticia!

Bud Schultz [Aurora West HS, physics]              Dropping magnets through pipes, revisited
Bud
recently obtained a set of 4 rather powerful Neodymium magnets [Item #35287 for about \$3] at a local outlet of American Science and Surplus [http://sciplus.com/].  These magnets were about 5 mm  ´ 7 mm  ´ 9 mm in size.  His presentation was an extension of those given by  Marilynn Stone, Don Kanner, and Bill Blunk, at  the Math-Physics SMILE meeting of 20 April 2004.  He dropped them -- first 1, then 2, then 3 -- through a vertical copper pipe 1.5 meters long, with an inside diameter about 12 mm --- standard half inch pipe. Its lower end was about 20 cm above floor level. Here are the times that we recorded for the magnets to descend and strike the floor, with various numbers of magnets attached together:

 Number of Magnets Descent Time 1 6.1 sec 2 7.9 sec 3 7.7 sec
The magnets fell very nicely without coming apart -- in fact it was difficult to pull them apart.  The magnets were slowed down because of eddy currents induced in the conducting copper pipe, producing an opposing magnetic field to slow down the magnets. as described by Faraday's Law and Lenz's Law.  Interestingly, the longest time of fall occurred with to two magnets.  As the number of magnets in the array is increased, the falling time changes because of  the increased weight of the array and increased opposing eddy current forces.

Bill Blunk repeated his demonstration of the Math-Physics SMILE meetings of 20 April 2004 and of 08 September 1988, dropping an aluminum parking token through two pairs of magnets -- a configuration commonly found in coin-operated vending machines.

22 February 2005: Brenda Daniel [Fuller Elementary School]          Magnetism and Electricity (handout from the FOSS Science Workbook)

This activity was completed with the help of small FOSS kits.  A FOSS kit is a small plastic board (about  20 cm by 25 cm). Several activities concerning electricity could be completed by inserting switches, batteries, wires, bulbs, etc. into sections preformed in the plastic board. The magnetism kit was a "baggie" with various items in it (some magnetic and some not) including a piece of magnetite -- a rock that could be picked up by a magnet (a surprise!).

Ed Scanlon asked us, "Why is it that both the North and South poles of a permanent magnet will attract a piece of iron, but the South pole of a permanent magnet will attract only the North pole of another permanent magnet, and repel its South pole?" Our discussion led to the explanation that there are microscopic magnetic domains throughout the iron, and we assumed that un-like poles attract and like poles repel. The magnetic domains are oriented every which way, so that their magnetic effects cancel out and the iron is not magnetized. Imagine such a bar of iron:

```                                        __________________
|                  |
|    NS-NS-SN-NS   |
|    SN-SN-NS-SN   |
|__________________|
IRON
```
Now when the North pole of a permanent magnet is brought near the iron, it attracts the South poles of the domains (and repels their North poles). This makes the domains in the iron re-orient so that their South poles point toward the North pole of the permanent magnet (and their North poles are repelled away).
```         _________________________         ______________
|                         |       |              |
|South Pole     North Pole|       |SN-SN-SN-SN-SN|
|South Pole     North Pole|       |SN-SN-SN-SN-SN|
|_________________________|       |______________|
Permanent Magnet                 Iron
(temporarily magnetized)
```
So the iron becomes temporarily magnetized with a South pole near the North pole of the permanent magnet. The result is an attraction between the permanent magnet and the iron. Similarly, when the South pole of a permanent magnet is brought near the iron, the domains re-orient with their North poles pointed toward the South pole of the permanent magnet, and the result is again an attraction between the permanent magnet and the iron. But that doesn't happen between two permanent magnets. The magnetic domains in a permanent magnet remain permanently oriented (or "frozen"), with their North poles pointing in one direction, and their South poles in the opposite direction. So, the North and South poles of a permanent magnet remain fixed at opposite ends of the magnet, and two permanent magnets will repel only when their like poles are near each other, and attract only when their un-like poles are near each other.

With regard to the electricity experiments, we talked about electricity in chemistry and biology.

• Chemistry:
• Electroplating.  For information see Electrochemistry Encyclopedia: http://electrochem.cwru.edu/encycl/art-e01-electroplat.htm.
• The "warning light" in the tank of a water softener. It indicates when the water softener is no longer removing metal ions from the input stream, because the conductivity of water in the tank becomes too high.
• Biology
• Electrical nerve impulses. These are rather different from ordinary electricity in wires -- for which the current is produced by the flow of electrons. Nerve impulses are produced by motion of ions, being more like waves of polarization and depolarization within the neural membranes.
22 February 2005: Ann Brandon mentioned that, at a recent meeting of the Illinois Section of the American Association of Physics Teachers [http://helios.augustana.edu/isaapt/] at UIUC, a magnet was dropped through a translucent plastic pipe with LED's attached across wire coils, which had been wrapped closely around the plastic pipe at several locations. As the magnet passed inside the pipe and through a given coil, the corresponding LED would flash. Now, there's Faraday's Law for all to see! Isn't that the Cat's Meow!

An excellent phenomenological exercise!  Thanks, Bud!

08 March 2005: Ann Brandon [Joliet West, physics]              Magnet Experiments
Ann
has a homebound student with MS this semester, so she developed a number of "take-home" experimental setups involving magnetism. Ann began by putting a bar magnet on the desk, and covered it with a large sheet of paper.  She place a small "toy" compass on the paper near the location of the magnet, and drew a short line on the paper to mark the direction of the compass needle (direction of the magnetic field).  Ann moved the compass in the direction of the field, marking the direction at each new location, and repeated the process several times.  She then connected the marks with a solid line, thus graphing a line of force of the magnetic field.  By starting at various positions, Ann traced out several lines of force for the magnetic field.  Next, Ann sprinkled iron filings out of a "salt shaker" and onto the paper.  The iron filings aligned along the lines of force that she had previously drawn. As the amount of fillings increased, the lines of force became three-dimensional.  Very interesting visual patterns!

Ann then placed two Ring Magnets on a wooden rod.  When the North (or South) poles of the magnets were adjacent to one another, the magnets repelled each another.  However, when the magnets had opposite poles adjacent, they attracted each other.  Ann then put several magnets on the wooden rod with the unlike poles adjacent, and held the rod vertically up. The magnets bobbed up and down slightly, coming to equilibrium positions.  Interestingly, the spacing between the magnets was greatest at the top, and least at the bottom. (Why?) Neato!

Ann pointed out that it is often possible to get End Rolls of Newsprint from local newspaper offices: e.g.

South Holland/Dolton Star - 6901 West 159th Street, Tinley Park, IL, 60477-1602
Phone: 708-802-8800 Fax: 708-802-8088
http://www.starnewspapers.com/.
End rolls may or may not contain a lot of paper, depending upon what's left over after printing. The printers office will often give them gratis to school teachers, or else at minimal cost. Thanks, Ann!

04 October 2005: Larry Alofs (Kenwood HS physics, retired)           Snake Eggs
Larry
said that they used to be called "magnetoids" (They are also called "magnetic hematite torpedoes",  "kissing stones",  "UberOrbs" and "snake eggs".), and they were a bit expensive (about \$ 80 for a pair, and obtainable only from England). This year he has seen them at flea markets for only \$ 4-5 each. They are two roughly egg shaped objects  6-8 cm long with the magnetic poles on the sides-- and not on the ends! They are powerful magnets, and due to their shape and structure their attraction and repulsion lets us do some really neat demos. For example, they may make a hissing sound when they come together.  When they are placed close to one another on a smooth horizontal surface, they jump, hiss, and spin around, and then stick together. How come? Can we breed our own? They can be ordered from various sources and are called "snake eggs" or "zingers".   Thanks for the show, Larry!