Bill Shanks (Joliet Central HS, retired; Joliet Jr College
titled his presentation: LED by the Light. So Bill lit up some LEDs (Light Emitting Diodes) for us. Pretty! He showed us how to do it for low cost. The LEDs were bought at Radio Shack (20 in a package for $2), and a battery holder (American Science Center for $ 0.50) and loaded it with 2 AA cells, which had been used in another application and were weak. The LEDs are rated at 2 volts and 20 mA, though they will light up at about 7 mA, he told us. Holding one up, he showed us that the long lead is the anode, the short lead is the cathode. (The big TV was connected to a miniature videocam to display a large image of small objects, and Bill frequently used this so that all of us could see clearly the small details on these devices. The videocam is available at the website http://www.allelectronics.com/) If connected in reverse, an LED won't light up. It is a diode, and will pass current in one direction, but not the other; it rectifies. Bill held up an AC-to-DC adapter that puts out various voltages: 1.5, 3.0, ...up to 12 v, bought at the American Science Center website http://sciplus.com/. Then he showed us an LED with 3 leads; the long lead is the cathode and the two short leads are anodes. When he connected the cathode to the negative end of the adapter and one of the anodes to the positive end, the LED glowed red. But when he connected the other anode to the positive end, it glowed green! If both were connected at the same time, the color was yellow! Appropriate to the Christmas season. Thanks for the good info, Bill, you sure brightened up our day!
Rich Goberville (Joliet Central HS)
showed us a bunch of physics "toys," that can be used to teach/learn. First was a colorful ball. He recalled the experiment in which the teacher throws a ball straight up and asks the class questions about its motion, such as: a) At the instant the ball loses contact with my hand, is its velocity positive, negative or zero? - Most students get this one correct and answer positive, since up is chosen as the positive vertical (+y) direction. b) Is the acceleration positive, negative or zero? - Most students answer that the acceleration is negative, since gravity acts downward in the negative vertical direction (-y). c) At the instant the ball reaches its highest point, is its velocity positive, negative or zero? - All students get this correct with the answer, zero. d) Is the acceleration positive, negative or zero? - More than half the students will say acceleration is zero!. Aha! They are mistaken, of course, since acceleration due to gravity is always downward and therefore negative; gravity does not turn off at the top! Now - Rich throws the ball up so it strikes the ceiling. But it sticks there for about a second! - then it falls down! "That is how it would look if the acceleration became zero when the ball reached its maximum altitude!" Rich tells them. Beautiful!
He showed us the novel behavior of the "sticky" ball a few more times. What a great way to make that point!
Rich then told us how, when he was younger, he pushed against a large (about 2 ft diameter) pipe to start it rolling downhill toward a creek where his younger brother waited to "catch" it. As it gained speed and neared his brother, Rich suddenly had an intuitive insight about what might happen to his brother - though he hadn't learned the word "inertia" yet - but before he could warn his brother, the pipe hit him! (He was hurt and suffered broken fingers - otherwise ok.) But Rich remembers his first intuition for inertia as developing from this incident.
He showed us a Chinese Yo-yo; then a Gyro-Frisbee (helicopter) launched by pulling a plastic stick that operated gears to spin its blades to high speed; a Balloon-Copter that was caused to spin by air from an inflated, attached balloon pushing out through jets at the ends of its blades; and a Balancing Bird! Then he handed out a smaller version of the bird, so we each got one. Available at low cost for a quantity. All these items came from this source:
Oriental TradingThey will send a catalog on request.
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Rich told us another story in which he got his brother to hold on to what amounted to a freely rotating gate. Rich managed to get it spinning fast enough that his brother's legs stretched out almost straight behind him - before he lost his grip and received a broken arm! Being Rich's brother wasn't easy! This was a lesson on centripetal and centrifugal force that he remembers. He then showed us a colorful sphere about 4 inches in diameter. When he held it up and made it spin by pulling a plastic strip. many colored (diode?) lights lit up inside, which was quite pretty to see. As the spin wore down, the lights gradually winked out. What made it work that way? An example of radial forces at work again?
Finally, he showed us a Skyliner. It was in the shape of an inverted L about a foot long, and he held it by its vertical portion as a handle. When he made its horizontal radius spin about its vertical axis, the end of its radius spelled out in glowing red the word PHYSICS in a circular band that appeared to be suspended in space. LEDs were being turned on-and-off in rapid sequence and persistence of vision resulted in the illusion. Available from
The Edge CompanyIt may be programmed to spell out a wide variety of messages. What a great set of ideas! Thanks, Rich!
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Keene NH 03413
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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!
Janet M. Sheard (West School, Glencoe)
gave us a three page copy of Planets of Our Solar System, which she printed out for us from the site of the Homepage that she created this past summer in the SMART program (http://www.iit.edu/~smart/). This lesson, which she originated for her students, is interactive, and to be appreciated it must be accessed live on her website: http://www.iit.edu/~sheajan1/lesson.htm She reviewed some of the features with us. It invites the website visitor (student) to participate in a "...magical journey of our solar system." There are six different Missions to attempt, which are of increasing challenge. For example, Mission II tells you to "...create a Power Point™ presentation about the solar system. Your next goal will be to develop a slide show for each planet. Each slide will have:
Speaking of unvisited planets, Porter Johnson mentioned the recent 6 hour presentation of the classic science fiction novel Dune by Frank Herbert. Details can be found on the Science Fiction Channel website http://science.discovery.com/sci-fi/10-sci-fi-books-of-all-time.htm#/10-sci-fi-books-of-all-time.htm [#8].
Her next project will be The Human Body Website.
Sally Hill (Clemente HS)
had two identical Tower of Hanoi puzzles on the table, and she invited a teacher and a student to come up front to solve the puzzles. Each puzzle is made from three dowel rods held vertically on a wooden base. The rods are in line and the distance between the 1st and 2nd is the same as between the 2nd and 3rd. (Draw a picture!) The 1st rod is surrounded by (sticks up through the holes in the center of) a set of 5 wooden rings which lie on top of each other and are at rest on the base. The bottom ring has the largest diameter, and each successively higher ring has a smaller diameter than the ring below it. The object is to move all the rings from the 1st rod to the 3rd rod. However, you may move only one ring at a time from any rod to another, and you may never place a larger ring on top of a smaller ring while making these moves. After the teacher and student had made some attempts, Sally gave a hint for the first move. It wasn't long and the student had out-paced the teacher! Isn't that the way it always works?! Anyhow, on the board, Sally placed hints for moves that looked like this:
number differencesPorter Johnson said a variation on this puzzle is the Chinese ring puzzle, or Cardan's Rings. [see the websites containing a Java Applet version of the Towers of Hanoi mazeworks.com/hanoi, an image of Cardan's Rings, http://www-groups.dcs.st-and.ac.uk/~history/Diagrams/Cardan's_rings.jpeg, and a brief history of math puzzles http://www.mefferts-puzzles.com/history.html.]
of moves in column
1 ring 1
2 rings 3
3 rings 7
4 rings 15
5 rings 31
Sally also gave us a handout of showing an X-shaped pattern of 9 empty boxes:
0 0Can you make the sum of each diagonal and the corners equal to 26? Use the digits 1 through 9 only once.
Thanks, Sally! (Got it yet?)
Notes by Porter Johnson