ISPP REMINDER

December 2004

OUR NEXT MEETING . . .

. . . is at DePaul University

Tuesday

Dec 7, 2004

6:30 - 9:00 p.m.

A map and directions are enclosed.

THE FREE GIVEAWAY . . .

. . . something you should find useful to excite student interest in physics - and who knows? - maybe even your own!

OUR NEXT FEW MEETINGS. . .

December 7 (Tues) DePaul Gerry Lietz/John Milton

January 19 (Wed) Elmhurst College Earl Swallow

February 17 (Thur) NEIU Paul Dolan/Joe Hermanek

March 16 (Wed) University of Chicago Kate Cleary/Van Bistro

April 12 (Tues) Lake Forest College Mike Kash/Bailey Donnally

AT OUR LAST MEETING . . .

. . . Kevin McCarron (Oak Park River Forest High School) welcomed us. Gerry Lietz (DePaul University) reminded us of the times of the next meeting at DePaul University (see above). Roy Coleman (Morgan Park High School) announced that NASA is having a High School design competition where students submit a well-written, focused paper that describes how our future society might adapt to the widespread use of Personal Air Vehicles (PAVs). The web site is at http://avst.larc.nasa.gov/competitions_high.html. Innovation Technologies is sponsoring the DuPont Challenge, a science essay contest who's web site is at http://www.glcomm.com/dupont/index.html. Roy looked at last year's senior division finalist (Juniors and Seniors) "Applied Physics and Plasma" and "Bovine Blood Giving New Meaning to Cowboy and Art". The Junior Division finalists were "String Theory: Bridge Between Quantum Mechanics and Relativity" and "Stressed Pigs Make Bad Meat". Gerry asked if there were any new people at the meeting for their first time. Bernoli Baello (Northridge Prep School) introduced himself. Anne Brandon (Joliet West High School) presented him with a New Teacher bag.

Gerry shared with us a note from George Austin at Francis W. Parker School who has a database of 12 years of questions that ran with a test-writing program called Make Test by Mountain View Inc. They have not upgraded the program to run on Mac OS X. George wanted to know if anyone knew of a newer test making program that might be able to access the questions from this data bank. If you have any ideas get in touch with Gerry and he will pass the information along to George.

Anne Brandon (Joliet West High School) passed out flyers announcing a series of workshops sponsored by NSF titled Physics Workshops for the Twenty-First Century. These three-day workshops are offered in February, April and June of this year. The February 24- 26 workshop for example is on Physics applets. Additional info can be found at http://tycphysics.org.

John Miller (Main West High School) started out with an overhead transparency that was out of focus. (we suspect on purpose) Jim Vokac (Oak Park/River Forest High School) stepped in and showed us how to focus the image without adjusting the projector. He placed a sheet of paper with a hole cut in it in front of the projected beam. The paper acted as a pinhole camera and though we could see only a portion of the whole projected image, it was in relatively good focus. Neat!

John described an experiment his students use in the lab to explore Newton's Second Law. A string attached to a cart passes over a pulley and a weight is hung from the other end of the string. Gravity acting on the weight provides a force to accelerate the cart. The students measure the acceleration for different weights and plot the results as force vs. acceleration where the slope of the line is the accelerating mass. Invariably the students will get too large a force for the observed acceleration due to the friction involved. Over the ten years that he has used the experiment John has tried various ways to eliminate friction. Recently he inadvertently took data while the cart was decelerating from an initial speed as the result of giving the cart an initial shove away from the pulley in the process returning the cart to its starting point for the next run. These results indicated the force acting was smaller than what he expected. Friction was working in the opposite direction of the weight force from the usual case. John found that if he drew a new line on the force vs. acceleration plot with a slope exactly between the lines plotted for motion toward the pulley and motion away from the pulley, the force came out exactly right where the slope agreed with the correct mass to with in 2%. Now he likes to have a lot of friction because of the interesting questions it brings up in the experiment. John admitted that there was a discrepancy ("a dirty little lie"?) in the experiment, which was that the tension of the string during the time the system was accelerating is actually less than the weight hanging over the edge.

Jim Szeszol explained that when he did the same experiment he would first add paperclips to the lower end of the string until the cart moved at a constant speed. In that way he compensated for friction. Ann Brandon (Joliet West High School) pointed out that if one plots the force vs. friction the line does not pass through zero. The value of the intercept is in fact a measure of the friction of the system. Roy Coleman (Morgan Park High School) suggested using a beaded chain over the pulley as a challenging variation to the problem.

John showed us his Einstein Action Figure available at the APPT on-line store at the AAPT web site http://www.aapt.org/

Jim Vokac (Oak Park/River Forest High School) played a segment of a video he found on the Internet "The Way Things Go" on DVD or VHS format for $20. It is a continuous chain reaction of Rube Goldberg types of contraptions that goes for 30 minutes. They make clever use of physical interactions and chemical reactions. It is sure to entertain and maybe stimulate some thoughts about physics. The web location is at http://www.buyindies.com/. Then type in "The way things go into the "Find" box in the upper right hand corner of the home page.

Gerry Lietz (DePaul University) shared with us a list of web sites for applets related to Fourier synthesis of waveforms. One in particular http://univie.ac.at/future.media/moe/galerie/fourier/fourier.html took the form of graphics equalizer like controls with which you can control the amplitude contributions of a series of harmonic frequencies with both sine and cosine phase components.

Two examples that were preprogrammed appear to be half wave and full wave rectifier waveforms. He called up the half wave rectifier and viewed the Fourier frequency components. The cosine frequencies had a large zero frequency component and several harmonic negative contributions at multiples of 2 and 4 times the fundamental and a significant sine contribution at the fundamental He posed the question of how to produce a DC signal from the half wave rectified wave form. One would merely introduce a capacitor resistor combination in parallel to the output, which Gerry noted, is a low pass filter. Gerry demonstrated this by altered the frequency components. Using the slider buttons he dialed all the harmonic components above zero frequency to zero. We saw that the signal that remained was a true D.C. signal. Gerry thought that this was a nice segue from filters to D.C. Power supplies.

Gerry called up a square wave. He noted that the signal was asymmetric about zero which in indicative of a sine function. The higher frequency components were sine functions with frequencies that were odd multiples of the fundamental. Gerry suggested a further exercise where students could use a square wave generator and mix it with a sine wave generator which will show beats at 3 times the fundamental and at 5 times the fundamental to show that indeed these sine waves are present in the square wave. John Milton (DePaul University) mentioned that there are many applets Gerry mentioned that Nick Drozdoff does a lot with physics and music and brings in students with musical interest Other sites are http://www.jhu.edu/~signals/phasorlecture2/indexphasorlect2.htm, http://www.falstad.com/fourier/ http:www.phy,ntnu.edu.tw/java/sound/sound/html, http://users.telenet.be/educypedia/electronics/javafoutier.htmand lastly http://www.see.ed.ac.uk/~mjj/dspDemos/EE4/tutFSFT.html.

Martha Lietz (Niles West) found a really cool mystery cup in her travels through China. The ceramic cup had a central post topped with a dragon's head. The cup was given to Chinese children to teach them moderation. If they filled the cup halfway it worked just fine. If the filled it all the way up to the dragon's head the cup suddenly sprang a leak and completely drained through the central stem. Can you guess how it worked? Martha passed out a handout that gave a little background to the cup. It is know as a Tantalus cup after the Phrygian King who was condemned in Hades to be placed in the midst of a lake that he could not drink from. The cup is said to have been invented by Pythagoras and therefore is also known as "The Pythagoras Cup of Justice". According to literature he too taught his students moderation, to not fill the cup completely to the brim lest it emptied itself through siphoning action. A source for the cup is at the web site www. wonderworkshop.com for $8.95. Martha made her own version using the top of a two liter pop bottle, a cork and a piece of rubber hose. She passed out a handout with details of how to make the cup and some history she found on the web.

Paul Dolan (Northeastern Illinois University) drew a force diagram for an object resting on a table. Is the normal force ever greater than the force of gravity pulling down? Paul explained that we could measure the normal force indirectly by adding a third force of a string pulling up. How large must this force be for the normal force to go to zero? We thought normally it would be equal to the weight of the object at which point the object would lift off the surface. Paul attached strings to a cup holding a metal weight and suspended the cup from a spring scale. Paul pointed out that one should be careful to first zero the spring scale, especially in the configuration you are going to use it in. The calibration would change if you used the scale horizontally for example. Paul showed that at one position on the surface of a folder he provided the scale read very small, less than a half Newton, and at another position on the same surface it measured 3 Newtons, much to our amazement. Gerry Lietz suggested that the surface might conceal a magnet which would change the force needed to lift the cup from the surface. Paul opened the folder to reveal a hidden magnet that increased the effective weight of the cup and its contents. Paul got this idea from one of his students Rikki Bickford.

John Milton (DePaul University) has difficulty convincing his students that if an object is at rest on a surface while a force is being applied horizontally the force of static friction is equal to the applied force. Another way to phrase the problem is the question "Is there a static frictional force if there is no horizontal force on the block?" Gerry Lietz asked, "How does static friction know how much to be enough to counter the pulling force?" Is there any way to make this concept clearer?

John hung a mass from a string and asked what the tension in the string should be. Then he allowed the mass to swing as a pendulum and asked if the force were different. John rigged up a Pasco force sensor to and obtained a plot of the force. When the mass was at rest the force sensor measured a value of 1.97±.01 N for a 200 g mass. When the mass rocked back and forth in the pendulum motion a variation of the force could be seen and John noted that the force at times exceeded the weight but at times also was less than the weight. How is that possible? John thought it was instructive to identify where in the motion the peaks and valleys occur.

John mentioned that there was a free video analysis program called Data Point similar to VideoPoint^TM available at http://www.stchas.edu/faculty/gcarlson/physics/datapoint.htm. In addition, video clips to analyze with this software are available to download from a Texas A & M University site http://www.science.tamu.edu/CMSE/videoanalysis/. John called our attention to another interesting site run by Dick Berg out of the University of Maryland called "Question of the Week" http://www.physics.umd.edu/lecdem/outreach/QOTW/active/questions.htm

He asked for a volunteer to support the pendulum and Raef Meves (Oak Park / River Forest High School) put out a supporting finger. John asked if he could feel the change in force as the mass oscillated. Actually we could see from the movement of Raef's finger that the force was changing dramatically. John had his students draw a free body diagram for when the weight was swinging at the top of its arc. Someone suggested inserting rubber band into the supporting string to visualize the tension changes.

Art Schmidt (Northwestern University) showed us an interesting toy. It consisted of a wooden cut out shaped like a bear with arms and legs spread eagle. Two strings, one on each side passed through each arm. Each string was tied at the top to the end of a dowel rod that was in turn supported by a single string tied to the center of the rod. The upper end of this string was tied to the ceiling and the whole array hung from this string. If you took the bottom ends of each string and alternately pulled on one and then the other the bear would shinny up the strings a distance of some two meters until it arrived at the dowel. Friction between the string and the wood holes through which the string passed

Jim Szeszol described an experiment his students do accelerating a bowling ball down a steel rail on the floor in the hallway. They can easily vary the speed of the ball at the bottom of the ramp by adjusting the height of the top end of the ramp. After the ball has left the ramp and rolls along the floor the students quantify the motion by timing the arrival of the ball at pre-measured locations. Jim found it useful to use a digital camera and pointed out that most digital still cameras can record a brief segment of video, which then can be easily transferred to a computer. The mass of the bowling ball has advantages; the most obvious is that friction becomes a negligible factor. Jim related how the ball will roll completely from one end of a long (150 ft) hallway to the other with very little loss of speed over the three minutes it took to travel the length.

Jim pulled out a few of his classic demos. He had tied a string to the center of a flat round rubber mat and dropped the mat on the floor. When he pulled up on the string the mat seemed to cling to the floor. As he pulled with a sideways force the mat moved along the floor but did not lift off. Jim slapped another mat onto the blackboard and it adhered to the board but still slide around in response to tugs on the string. A partial vacuum was formed between the mat and the surface such that the atmospheric pressure held the mat to the surface. Jim asked for a volunteer and convinced Bernoli Baello (Northridge Prep School) to help him out. Jim gave him two items, a sack of something and a solid object and asked which had a greater mass. Bernoli couldn't decide. Jim explained that a person cannot detect a difference of less than 10% in the relative weights of two objects and that these two had a mass difference of 1.1 to 1 kg. Jim had taken apart a K-Mart bathroom scale and glued a new dial over the one in units of ponds that came with the scale, calibrating it in Newton's. Simple enough! Then he showed us a bathroom scale that electronically displayed the weight on a hand-held readout for people who might not be able to read a normal scale when standing on it. The remote read-out also included the option to change the calibration from pounds to kilograms. Jim tired to come up with some relationship that students could easily remember to grasp the magnitude of weights in the SI units. He calculated that 1 Newton is about 0.23 lb or around a quarter of a pound. Hence, a quarter pounder could be called a Newtonberger??

Jim shared with us some of his musings at odd times of leisure by asking us why it is easier to separate a single sheet of toilet paper off the roll when the roll is new than when the roll is almost empty. We suggested that the roll has a great inertia with the whole roll. While the idea is simple, there was much more to this example. Jim, who is a master demonstrator, was also showing us how to present a demonstration in an engaging way. As he posed his question he carefully and patiently ripped off at least twenty squares of toilet paper from the roll, each with careful attention. After about the 10th sheet we couldn't help but wonder what he was doing. Was he crazy? He had our attention. We were hooked! Very nice, Jim!

Following along the same theme of inertia Jim took a 2 m PVC pipe that was stuck through a wood block. The block consisted of two pieces each with half a hole cut in them bolted together around the pipe. Jim used to use just a single block with a hole drilled through, but humidity would alter the hole size slightly and the block either would bind or be too loose. With the bolts holding the blocks together around the pipe, Jim could adjust the grip just right. Jim held the pipe vertically and pounded the bottom end on the floor repeatedly. The block slowly inched its way down the pipe. Was gravity pulling the block down? Then Jim rapped the top end of the tube several times and the blocked climbed its way back up. Hmm? Art Schmidt (Northwestern University) suggested Jim hold the tube horizontally to remove any doubt about whether gravity doing the moving.

Jim continued on the inertia theme showing us his classic coat hanger seasonal decoration. Jim bent a coat hanger into an "M' shape and hung ornaments on the ends. He then balanced the thing at the central point of the wire on his head and showed how the hanger remained stationary as he turned his head from one side to the other beneath it. Jim pointed out the utility of the hanger in that you can change the items you hang on the ends to match the season and/or your mood. Ornaments work for the Holiday season. Bring out hearts on Valentine's Day: bunnies at Easter.

Jim hung two pear shaped objects on the ends and announced a balanced system with a pair of forces. He reached inside one of the fruits and pulled out two "F"'s and reminded us that forces come in pairs?

Jim mounted a ticker tape timer to the end of a slot car track. He asked how far would the car accelerate? He showed us the analysis of the data. The data showed a very uniform acceleration over the first 25 cm.

Bill Shanks (New Trier High School) showed us an ad for digital multimeter at Harbor Freight for $3.99. Bill recalls paying $80 for an analog multimeter. Larry Alofs pointed out that he saw a 6-inch digital calipers at Harbor Freight for $16. At least some things have gone down in price over the years.

Raef Meves (Oak Park / River Forest High School) showed us a demonstration he uses to illustrate the difference between weight and mass. He hung 500 g mass on a spring scale and showed that it deflect indicating weight. Then he proposed leaving the earth. What would happen different? He attached the mass to a second scale and it read zero weight. Then he moved over to simulated "planet" which looked to us like a large cardboard box. As he approached the planet the spring scale began to register the weight of the mass. The mass existed all the time but the weight came only in the gravitational field of the "planet". He pulled off the box and revealed a large magnet that had provided the simulated gravity. Catching!

James Chichester (Oak Park/River Forest High School) showed us a force table that he built for $5.50from a circular piece of pre-cut particleboard and some dowels. He passed out a sheet describing the tolls and parts list with instructions to build the table. It took him about two hours once he got all the equipment together. On the flip side he included a copy of the exercise he designed for use with the table. James demonstrated how easy it was to move the scales around to set up different geometries. This seems to work very nicely.

Debbie Lojkutz (Joliet West High School) had her students pick an Olympic event to design a poster around, and show how they relate it to physics. Each student then gave a short presentation to go along with the poster. Some of them were quite clever. She noted the arm on the swimmer doing a backstroke In The Physics of the Backstroke Poster actually moved. Students were given a month to work on the project. Debbie laid out several posters for us to look at.

Kevin McCarron (Oak Park/River Forest High School) explained our free giveaway for the evening. Kevin use a lathe to make a bunch of wood pears which he then cut in half. Each of us could claim a pair of pear halves to complete at our leisure. Kevin held up a finished pair, or is it pear? He opened the two halves and he had painted two large block letter F's on each half. Yup! Forces come in pairs. Kevin had prepeared several varieties depending on how you wanted to connect your pair. They could be pinned, doweled or connected using magnets. He also provided paint to paint the outside a pear color. Thanks

With that the meeting came to an end. Submitted by Arthur Schmidt

For any information regarding ISPP contact Gerry Lietz at DePaul University, Physics Department, 2219 N. Kenmore Chi. IL 60614 phone: 773-325-7333 e-mail glietz@depaul.edu. ISPP home page: http://condor.depaul.edu/~glietz/ispp/ispp.html

BRING FRIENDS BRING IDEAS! ! SEE YOU THERE !! !

John Milton /Gerry Lietz 773-325-7333 Mike Kash Earl Zwicker

Van Bistro / Kate Cleary Pete Insley Earl Swallow

Ann Brandon/Debbie Lokutz Roy Coleman Tom Senior

Jan Dudzic David White Kevin McCarron

Art Schmidt Chris Chiaverina Paul Dolan

Gordon Ramsey Ruth Goehmann Marie Baehr

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During 2004 - 05

Coordinators: Paul Dolan

Gerry Lietz

Earl Zwicker

ISPP Authors: Gerry Lietz Data Base Managers: Roy Coleman

Art Schmidt Earl Zwicker

John Milton

Pete Insley

Photographers: Paul Dolan Treasurers: Ann Brandon

Art Schmidt Peter Insley

Gerry Lietz

John Milton

Special Events Committee:

Physics Day - Ann Bradon, Roy Coleman, (Co-Chairs)

John Rush Award - Debbie Lojkutz(chair) Martha Lietz, Eileen Wild, Bill Blunk

Harald Jensen Award - Keith Bellof (chair), Martha Lietz, Ann Brandon

Annual Tri - Physics Meeting - Bruce Illingworth, Gerry Lietz

New Member Committee - Kevin McCarron (coordinator), Ann Brandon, Pete Insley, John Milton

National Bridge Building Committee - Carlo Segre

To get to DePaul University:

From the north and northwest

From the Kennedy Expressway (I-90/I-94) exit at Fullerton Avenue and turn left (east.) The Lincoln Park campus is approximately two mile from the expressway on Fullerton Avenue at Kenmore Avenue.

From the west

From the Eisenhower Expressway (I-290), turn onto the Kennedy Expressway (I-90/I-94) heading toward Wisconsin. From the Kennedy Expressway (I-90/I-94) exit at Fullerton Avenue and turn right (east.) The Lincoln Park campus is approximately two mile from the expressway on Fullerton Avenue at Kenmore Avenue.

From the south

From the Dan Ryan Expressway (I-90/I-94) continue as the expressway becomes the Kennedy Expressway (I-90/I-94). Exit at Fullerton Avenue and turn right (east.) The Lincoln Park campus is approximately two mile from the expressway on Fullerton Avenue at Kenmore Avenue.

From Lake Shore Drive (north or south)

Exit Lake Shore Drive at Fullerton Avenue. Head west for approximately three miles. The Lincoln Park campus is located at Fullerton Avenue at Kenmore Avenue.

Vouchers will be available for parking in the high rise lot.