Fred Schaal (Lane Tech HS)
told us how he was advised to use rubber cement to hold handlebars on his bike together - but the cement seemed to behave more as a lubricant, and didn't serve the purpose. What will work? Any ideas?
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!
Don Kanner (Lane Tech HS)
showed us an article from the Onion, a satirical newspaper from Madison, WI, spoofing the Kansas School Board of Education's rejection of evolution. His point was - what do you do if what you are teaching in science is against a student's religious views? Some students feel religion and science are incompatible. Don cited the view of creationists that the earth was created something like 5000 or so years ago, or in 6 days by the Bible, while science believes that the universe started with the Big Bang more than 10 billion years ago. Don wrote down Einstein's equations from special relativity for relative velocity and time dilation, and used these to argue that if God operates near the speed of light, then the viewpoints of religion and science may agree. Thanks for a fresh viewpoint, Don!
Bill Shanks (Joilet West HS, ret)
held up a starter used with fluorescent light fixtures. It is a cylinder about 4-5 cm long and about 2-3 cm diameter. He took it apart to show us that the inside apparently had two parts, something that looked silvery in color (mercury?) on the inside, and the other was maybe some sort of small coil. Bill asked, "How does it work? What are these parts? What does it do?"
In the discussion that followed, someone pointed out that a fluorescent bulb has filaments at each end, and the starter causes current to flow in the filaments, making them hot enough to vaporize mercury in the tube, so the mercury could then be ionized by the high voltage (supplied by the ballast, ie, high voltage transformer) applied across the tube. Once the mercury is ionized, the ions give off light when atoms go back to states of less energy. The light energy, mostly not in a useful visible range, then reaches the phosphors coating the inside wall of the fluorescent bulb, and the phosphors then absorb that energy and emit light in a useful range for us to see by. Rapid start fluorescent bulbs do not require starters (which eventually go bad), apparently because the ballasts provide a voltage high enough to ionize the mercury vapor that is present at room temperature. Maybe someone will supply us with definitive answers about how fluorescent bulbs and their fixtures work at a future meeting?
This got us into a discussion of possible dangers of fluorescent bulbs - the hazards of mercury. Many of us recalled "playing" with silvery liquid mercury in our classrooms found in the barometers. And Earl Zwicker remembered how his 8th grade science teacher heated a red, powdered solid (mercuric oxide) in a beaker and it turned into the liquid, silvery mercury. Lee Slick told us that oxygen is driven off, and if it was captured, this was an easy way to get oxygen for use in experiments. Earl pointed out that mercury vapor from the liquid was very dense, and stayed close to the floor. The most dangerous forms of mercury are in the form of organic compounds which can be ingested. Manufacturing processes may put mercury into rivers and lakes, and it may be ingested by fish as organic compounds. Then we (and other creatures) eat the fish. Ann Brandon pointed out that not long ago - and even these days - we had warnings not to eat too much fish from our lakes, because of the hazard of mercury. But she said that fish that were caught during the early 1800s - before manufacturing processes could have put mercury into the water - showed much the same levels of mercury being found today!
Bill Shanks drew a diagram on the board showing a "motor" consisting of a battery, a pool of mercury, and a spring suspended above the pool with its bottom end touching the mercury pool surface. One terminal of the battery was connected to an electrode placed at the bottom of the mercury pool, and the other terminal to the top end of the spring. A current would then flow, the coils of the spring would be magnetically attracted to each other - causing the spring to shrink - which moved the spring out of contact with the mercury pool, interrupting the current. The spring would then relax to make contact again, and the cycle would repeat, making the spring jump up and down. What about mercury vapor that was released into the classrooms where this experiment was done by science teachers? Who knows?
pointed out that the Mad Hatter in Alice in Wonderland was mad from the effects of mercury used in the manufacture of hat bands. Apparently this sort of thing really happened in the past! Lee also informed us that mercury cost about $60 per pound about 5 years ago.
After that interesting digression, Bill Shanks held up a copy of the text for an Astronomy course he is taking
Michael A Seeks
Horizons [6th Edition]
Brooks/Cole Thomson Learning
511 Forest lodge Rd
Pacific Grove, CA 93950
They're studying about Astronomical Influences on Earth's Climate, among other topics. Bill told us about a researcher, Milankovitch, who wrote and made predictions in the 1920's about relatively small changes in earth's orbit, such as its shape, precession, and nutation. which would couple together with a periodicity of about 10,000 (?) years, making changes in how solar energy reaches earth, and triggering ice ages. For interesting web-based references see the websites
Porter Johnson told us that variations in energy from the sun (sun spot activity variations and other processes) probably were more important. He pointed out the apparent connection between the disappearance of sunspots (Galileo) and a little ice age.
Ann Brandon (Joliet West HS)
held up a bunch of AAPT Product Catalogs, 1999-2000 edition, and gave them away to us, reading to us some of the useful things that were available. Ann also invited us to get our students involved in the Physics 2000 Photo Contest, and showed us one of last year's winners, a photo of a Coke Can balancing on edge. And we also received an ISAAPT Flyer. Thanks, Ann!
Porter Johnson (IIT)
told us about a vacation trip which took him through Pestigo, WI. At the same time as the Great Chicago Fire, there was an even greater fire around Pestigo, which was a much greater disaster than the Chicago fire in terms of lives lost and destruction of property and farm animals. There was a sign in Pestigo which marked a feature in common with Traverse City, MI and Egg Harbor, WI. What is it? The 45th parallel! The sign said that the person reading it was half-way to the North Pole from the equator. But - according to a second sign a little North of Pestigo - if one accounts for the fact that the earth is not a perfect sphere, but has the shape of an oblate spheroid (flat at the poles and bulging at the equator), then one must travel a little farther North of the 45th parallel to really be half-way to the North Pole in terms of travel on earth's surface. Porter proved that this was wrong (and showed us at the board that the halfway point is South of the 45th parallel!), but was too polite to let them know they are in error. Fascinating!
What a terrific meeting! Don't miss the next one!
SEE YOU THERE!
Notes by Bill Colson, Sally Hill, Lee Slick, Porter Johnson