High School Mathematics-Physics SMILE Meeting 1997-2006 Academic Years Mechanics: Miscellaneous

30 September 1997: The first presentation was made by John Bozovsky [Bowen HS], featuring a virtuoso performance by Ernest the Dancing Bear. Ernest avidly rode his bicycle back and forth on a rope that was held at the ends and moved up and down by two people. As a variation, a "spit motor" [i.e. rotisserie motor for a barbeque grill] was outfitted with a rotating arm at one end of the rope, the other end being clamped in a fixed position. It was the judgment of the group that the device needed a longer arm, a shorter span, and a faster motor, and there was elaborate discussion of these points.

It must have been "science" as it did not work as expected. Ernest would not respond as he should or was expected to. Ernest is a bear doll sitting on a motorcycle with his feet permanently attached to the pulley with two balancing bars that are to keep him balanced on a wire. The problem is that there was too much friction mainly due to the cloth of the bear's pants.

`              - The setup that failed              The arm on the motor was about 10cm long`

It failed; probably due to these effects:

1. Stretched string sagged too much -- need stronger stuff
2. The arm was too short and should be longer
3. Too much drag on the pulley

The pulley on the road being lifted and dropped is to move the toy on the pulley

14 October 1997: Bill Blunk [Joliet Central High School]
He described a Force Stick, available from the Science Kit Catalog [http://sciencekit.com/] as item # 45444 for \$13.75. The device reads force, and it has a sliding sleeve that records the "maximum force". It is calibrated for acceleration by attaching a standard mass to it. It is rather more portable and user-friendly than the usual "accelerometer", and much more durable. He tested it by dropping it with a "suction cup bottom" attached, and looking for the maximum displacement, and also with a "super ball bottom". It seemed that in the second case the maximum force [acceleration] was about twice as large as in the first case. The device also properly recorded centripetal acceleration as inward bound.

27 October 1998: John Bozovsky [Bowen HS]
He passed out a cardboard fish and cut a slot from the center through the tail. He placed in a dish of water and place a drop of "Fish Go" in the slot and the fish was propelled by the substance exiting the slot in the tail. The "Fish Go" fuel turned out to be Three-in-one machine oil, and the fish was propelled because of Newton's Third Law, like a rocket.

02 February 1999: Alex Junievicz [CPS Substitute]
He showed the only good pot-hole. The problem is with a wheel to try to get out of the pothole Speed is the first thought, but actually there is less movement as the speed is increased---the only way is rock--getting momentum.

He also showed a give-away that had a front surfaced mirror and behind is a regular mirror....Every second reflection can be noticed by the brightness-color of the image. First showing the sandwich covered by a box, and removing the box and still seeing the progression of the image still being the same. Another sterling way is showing it by holding it in front of the body.

Another comment was that a math teacher allegedly got severe eye damage at Juarez HS because a student pointed a laser at her eye.

02 February 1999: Cynthia D'Souza [DeLaSalle High School]
She worked on a NSF project during summer

`                    Pre-Lab                    After Lab                    Loop`

She had several stations that had a ramp of at least 30 cm high and had at least 20cm of table on which the ball rolled. A photo-gate that was attached to a computer that was programmed to measure the time the ball obscured that photo-gate and calculate with the known diameter of the ball and respond with the velocity of the ball just before it left the table.

One problem was that the steel ball provided had a tendency of bouncing as it rolled on the table. Another problem was noted by the receptor of the ball that had some height. Still another problem was where to measure to the cup which the rules indicated the ball should not touch the sides. One group substituted the given steel ball with one of the Happy-Sad type balls.

Knowing the velocity of the ball leaving the table, it was simple to compute the time that the ball took to fall the distance from the table down to the top of the can and then knowing the time, calculate the distance laterally that the ball would travel till it hit the cup

02 March 1999: Walter O McDonald [CPS Substitute]
He brought in an manipulative he purchased at Robot World in the Wisconsin Dells.

It was a little difficult to see why the figure was called "Moons of Jupiter" because it was a pendulum driven by a battery mechanism. In the base there is a driver coil activated by a transistor keyed by another sensing coil. When a magnet passes the pickup coil, thus triggering a power pulse (in the coil this causes a magnetic pulse) pushing away the magnet in the pendulum.

`  `

The main pendulum is on the stand and there are attached to the pendulum two other sets of balls that rotate on their own pivot pulse. As the pendulum swings the smaller set of balls on each side of the pendulum would spin in a chaotic-appearing form.

Discussions of rotational and frequency formulas were noted. The period seemed to be about 1.4 seconds and trial of stopping the secondary ball seemed to indicate the additional movement caused the main pendulum to have less amplitude as the secondary balls were active.

Porter commented that Chaos [http://www.physics.orst.edu/~rubin/nacphy/JAVA_pend/CHAOS/] can occur only when there are at least three degrees of freedom. For our case, we have the motion of the main pendulum, the oscillation of the weights on the right side, and the motion of the other set on the left side. The balls on the left were affected by a magnet reacting with the set on the right.

We did not see why it was sold with the Jupiter name, but Jupiter is often used by NASA as a way to "sling-shot" satellites on into outer space. See the website http://www.jpl.nasa.gov/basics/bsf4-1.html [click on lite gravity].

16 March 1999: Louis Harmon [ST Barbara HS]
She teaches at a girl's school, and has a small class and can do more advanced subjects. She showed a way of teaching addition of vectors (girls school - Jump ropes and a scooter {an item from the gym that has 4 wheels - maybe to drag equipment in the gym} someone sits on the wheels and with 2 jump ropes  are pulled so the resultant can be seen.. Another way of changing friction was to move around in the gym with shoes, socks, and barefoot.

06 April 1999: Earl Zwicker [IIT, retired]
He produced a box postmarked 07 January 1982, sent to him by Harold Jensen, Professor of Physics from Lake Forest College and Chicago Area Physics Guru. Inside the box was a perpetual motion machine, in which a magnetic top would spin on a relatively rough surface, and run "for as long as you like" without stopping. [The device had been ordered from a Johnson-Smith Catalog; they are still being published! http://www.johnsonsmith.com/]

Earl raised the question "how does it work?". He also produced a similar device out of the SMILE office, in which a "whirly-gig" actually picked up speed as it rotated while moving along a track. How can you disprove that these devices are true perpetual motion machines without taking them apart?

04 May 1999: Earnest Garrison [Chicago Vocational High School]
He brought in a hi-tech Yo-Yo. How could an old thing as yo-yo be made high tech? The answer to the new yo- yo's is that they have a clutch operated by a speed regulator that allows you to "walk the the dog", and when the speed drops the clutch engages and up comes the yo-yo. Also as a hi-tech feature, they have lights that flash and a sound that is made; some even depend on speed. It is surprising that such an old concept is still enticing the youth.

Porter made a comment about the yo-yo variation called the diabolo, which consists of two sticks and a string with which you spin a spool of a certain size and weight. Once you get it to spin fast enough you can throw it in the air, and if you are good [like me! -PJ] you can catch it back on the string! Amazing, but not impossible! The game was invented by the Chinese over 2000 years ago, and brought to Europe by French and English expeditions, and given the name diabollo [ancient Greek, "through throw"]. Pictures and details can be found on the following webpage: http://www.juggling.org/help/circus-arts/diabolo

07 December 1999: Arlyn Van Ek (Illiana Christian HS)
showed us a beautiful bird, made of wood, from Costa Rica. Its wingspan was about 2.5 ft, and its wings and body (separate parts) were suspended by strings from a wooden rod. When Arlyn gently moved the bird up and down, he could - by timing the motion correctly - cause its wings to "flap" up and down on each side of the body. He then held the rod still while the motion continued and gradually died out. "What physics is involved in this?" is the kind of question Arlyn asked. Some answers we made:

• conservation of momentum;
• forces;
• harmonic motion.
One of us asked: Does this cause quite a flap in class? -- which provoked some slight smiles, but which Arlyn judiciously ignored. An unusual approach to help students make connections between physics concepts and reality!

11 April 2000: Bill Blunk (Joliet Central HS)
had his miniature video camera connected to the big TV in front of us, and he placed a black cube-shaped device (about 2 cm on a side) mounted on a flat metal plate (about 6 cm x 15 cm) on the table. Then he told us about a kindred cross country skier, Bert Kleerum [Eagle River Nordic Skis] and their interest in measuring accelerations encountered in skiing. This has never been done before. They are trying to find a way to do this, and the black cube is an accelerometer used to measure and control airbag deployment. Obtainable through David Vernier [a premier supplier of sensors and electronic displayers and recorders for physics teachers - see any physics teacher on this, or else check the website http://www.vernier.com), and capable of +/- 5g, a very useful range. Bill showed us his Palm Pilot, a pocket size device with a graphic display and capable of recording much data. He focused his video camera on its display, so we could see it quite clearly on the large TV. Another device, which plugs into the Palm Pilot, is made by Imagiworks http://www.imagiworks.com, and Bill plugged the black cube accelerometer into it in turn.

Earl Zwicker gave Bill a hand by moving the accelerometer in various ways: circle, back-and-forth linearly, up-and-down linearly, accelerate and stop linearly - in opposite directions. Each of these motions resulted in a graphical display which we easily saw on the large TV, as Bill held the video camera focused on the Palm Pilot. (Which of the motions looked like a sine wave?) It is more compact than TI-CBL, with greater memory. And the Palm Pilot easily dumps its data into a PC to be analyzed by EXCEL. Now - the skier would carry the Palm Pilot in his jacket, connected to the accelerometer mounted on a ski, to record the physics of the ski's motion.

But - Bill still needs to find a way to record position as the skier moves along. This might be done with a permanent magnet under the snow, with a pick-up coil on a ski. The motion of the coil-on-the-ski through the field of the magnet would result in an electromagnetic induced pulse or "blip" to be recorded by the Palm Pilot on top of the acceleration data. Bill had a strip of refrigerator magnet material which could be placed under the snow, but a pick-up coil of about 200 turns of no. 26 wire did not produce a sufficiently strong signal. What to do? Any ideas? Could the difficulty be caused by an impedance mis-match between pick-up coil and the Imagiworks gadget? Let Bill know if you have an idea that might work. Terrific, Bill! Keep us informed!

Post-hypnotic thought/suggestion by PJ: What about just hooking up a GPS device to the calculator, and have it record the position? You can set it for "relative" position, relative to the starting point, and it is pretty accurate on that basis. But, is it accurate enough??

02 May 2000: Janet Sheard (West School, Glencoe)
showed us Build It, Move It, a kit on Force and Motion (ETA catalogs)/ 4th grade. She said the materials could be adopted to a wide range of levels. The inexpensive but effective apparatus came in a plastic storage box. Many investigations into forces: What are they? Sources of? Motion, Friction, Inertia, Machines. Janet had not yet used the kit, and we ran out of time, but maybe Janet will show us how some of it works next Fall. Essentially "Physics for Every Kid." Inspiring!

23 April 2002: Fred Schaal (Lane Tech HS Mathematics) -- Top-ological Theory and Planetary Lineups
Fred
dealt with "top"-ology at an extremely applied level, showing a molded plastic top that has a smooth curved bottom, with a projecting shaft on top.  Holding the top by its stem, Fred set it spinning about its axis of symmetry with its bottom on the table. To the amazement of many of us, the top turned itself over, so that it was spinning on its stem!  How come?  Fred also showed us that the top would initially rotate "upside down" when set into motion in that orientation, and would stay that way.  This physics toy, which is called a "tippy top", has identical moments of inertia about directions perpendicular to its symmetry axis. The top continues to rotate in the same sense when its flips, so that the angular momentum of the top does not change direction.  This is different from the "rattleback", which has three different moments of inertia, and for which the direction of rotation may change.  For details concerning the tippy top, see http://en.wikipedia.org/wiki/Tippe_top and especially the American Physical Society page  http://www.aps.org/units/fed/newsletters/fall2001/kamishina.cfm, which contains the following excerpt:

"Among a variety of tops, a tippy top is most popular. At a glance, a tippy top is hardly distinguishable from normal tops. A top usually rotates steadily around the rotational axis and the rotational axis rotates around the vertical axis as everyone knows. However a tippy top turns upside down while rotating.
at rest --- rotating
(Images courtesy of http://www.aps.org/units/fed/newsletters/fall2001/images/). The big difference between them is that the usual top falls down when at rest while a tippy top doesn't. It is stable at rest. This means that the center of mass of a conventional top is situated higher and it is therefore unstable at rest, while on a tippy top the center of motion is at the lowest position at rest. Roughly speaking, rotational motion progressively lifts the center of mass of a tippy top, and finally turns it over. The mechanism by which the axis of rotation gradually moves up or down in addition to a precession, moving in a circular cone about the vertical axis, is in large part connected with the action of friction at the point of contact with the floor."

"The quantitative explanation of this mechanism is too difficult for students to understand. The qualitative explanation is more suitable for children. To reproduce the motion of a tippy top, I showed a 2-dimensional tippy top consisting of a large ring and a small ring both made of metal wire The two rings are attached at a point with the small ring inside the large one on the same plane. The role of the smaller ring is to shift the center of mass of the system away from the center of the large ring. When you rotate the large ring around the vertical axis connecting two centers of both rings with the small ring at the bottom, the system acts like a tippy top. While when you do the same thing but with the small ring at the top it acts like a conventional top. The difference in behavior is the position of the center of mass of the system."

Fred also alerted us to the fact that the planets Jupiter, Saturn, Mars, Venus, and Mercury are aligned in the Western sky just after dusk.  For the next two months, 8:30 pm is about the best viewing time  For details see http://www.adlerplanetarium.org/index.shtml.  If you miss this planetary display, you can catch it again for a repeat performance in about 40 years!  Thanks, Fred!

23 April 2002: Bill Blunk (Joliet Central HS Physics) -- May the Force be Wilber!
Bill
set up a Wilberforce Pendulum [mentioned at the last SMILE meeting], in which there are two degrees of freedom, corresponding to "up-down" motion of the mass suspended by a spring, as well as its "torsional" motion.  When he started the pendulum in an "up-down motion", its motion gradually became torsional, and then went on to switch slowly but steadily back and forth between "up-down" and "torsional" motions.  How come?  Bill assured us that, since April Fool's Day has passed, this was not a trick, and showed us that there was nothing up his sleeve.  We discussed the matter at length.  A vibrating system with two degrees of freedom with normal modes lying at slightly different frequencies will execute periodic motion only for very specific initial initial conditions.  Otherwise, one observes "beats" between the two normal modes, in the same spirit as two tuning forks of slightly different frequencies.  There is coupling between "up-down" and "torsional" motions in this case, so that neither of these motions corresponds to a normal mode of the system, as one might think.  We decided to look for this coupling in the "static" case in which the mass was not moving, making for slightly different values of the suspended mass.  To our surprise, the equilibrium position of the marker on the mass could be seen to rotate as the suspended mass was slightly changed.

You no longer have to beware the dark slide, Bill!

21 October 2003: Wanda Pitts [Douglas Elementary School       Inertia Challenges
Wanda let us through the following exercises to illustrate the concept of inertia:

• COIN DROP:  a coin on an index card supported by a drinking glass drops into the glass when the card is quickly snapped away by flicking with an index finger.
THE LOOP: a round loop (made of manila folder cardboard) is placed on top of a drinking glass.   A coin resting is placed on top of the loop at the center.  When the loop is knocked sideways with a ruler, the coin drops into the glass.
• KARATE CHOP:  a pen held vertically has a flat ball of clay at its top, which serves as a table. A narrow strip of writing paper is held by the other hand, so that it rests on top of the clay at the other end.  A coin is placed on top of the paper over the clay. When the paper is rapidly removed by striking it vertically with a ruler, the coin remains in place on the clay table.
• TOWER TAKE DOWN: stack of coins on a flat surface. Use a thin ruler or index card to snap the bottom coin away without moving the others. A slow motion, either with the ruler or the index card,  would carry the stack of coins with it.

Ken Schug added another example involving inertia, using a roll of toilet paper.  With a slow pull the paper rolls, whereas with a fast pull one piece detaches. Place an object on the end of the toilet paper on a flat surface, and then pull slowly  (object travels with paper) or rapidly (paper detaches). Note that, as weight of object is increased, the paper eventually will detach, with even a slow pull.

We all had fun and learned a lot! Thanks, Wanda.

18 November 2003: Karlene Joseph [Lane Tech Park, physics]        Launching Your Marbles
Karlene
showed us an inquiry-based learning exercise obtained from her colleague Brian Scane.  She passed around paper bowls and plates, as well as marbles. Karlene asked us to put a marble in the bowl, and make the marble move in a circle within the bowl. After some practice, most of us were able to make the marble go around in the bowl, although if the marble left the dish, it appeared to move oddly. In particular, when the marble left the bowl it moved in a straight path, even though its motion had been roughly circular before its departure.  We also tried the same exercise with a paper plate.  It was much more difficult to get the marble to stay on the plate.  Finally, she asked us to cut one quadrant out of the plate, and predict how the marble would move when it left the plate after making three-quarters of a revolution.  Good physics insights, Karlene!

09 December 2003: Don Kanner (Lane Tech HS Physics Teacher)      Forces
Don
had a modified version of Gary Guzdziol's vacuum disk [mp111803.html]. By reducing the internal plastic disk's diameter, it was used as a washer for a nut on the end of an eyebolt to which a heavy cord was attached. Without the worry of string breaking, Don appeared to lift a stool with the device but left us wondering which force really lifted the stool.

Don also posed the challenge of how to get all the marbles to stay on a paper plate when the plate is rotated, as an extension of the lesson given by Karlene Joseph at the last SMILE meeting [mp120203.html]. Go for it, Don --- you're on a roll!

09 March 2004: Walter McDonald [CPS Substitute -- V A Technician]          Questions that Involve Sailing
Walter
posed some questions that involved determining the direction of motion of a sailboat, when the directions of the wind velocity and the water current, as well as the orientation of the boat and location of the sails, were specified.  These questions appeared as exercises 877-980 (questions on p 303; answers on p 402) in the innovative book 1000 Play Thinks:  Games of Art, Science, and Mathematics by Ivan Moscovitch [http://www.zephyrpress.com/].  Roy Coleman mentioned this book in the Math-Physics SMILE class of 24 September 2002mp092402.html. Here is a brief paraphrased sample of questions and answers:

 Question: Answer: If you are sailing downwind in a 40 km/hr breeze, with your sail making a 90° angle with the keel of the boat, what is the  fastest speed you can achieve? Less than 40 km/hr. At that speed, the sails sag, as they would on a windless day. If you are sailing downwind in a 40 km/hr breeze, with your sail making an angle of less than 90° with the keel of the boat, what is the fastest speed you can achieve? Less than before, since the sail catches less wind, and the force on the sails is not in the direction of motion of the boat. If you are sailing crosswind in a 40 km/hr breeze, with your sail making an angle of less than 90° with the keel of the boat. Can you sail faster than in a tailwind? Yes, since the sail does not catch up with the wind, as in the first case. How do you get a boat to move forward during a headwind? By tacking, or sailing on a zigzag course at an angle to the direction from which the headwind is coming, with the sails opened to catch the wind.

From now on, it will be smooth sailing for all of us.  Very good, Walter!

23 March 2004: Wanda Pitts  [Douglas School]         Spinners
Wanda
began this lesson on Physical Chemistry by asking us about inertia.  We pointed out that inertia is the tendency of an object to resist a change in its motion.  Next she placed a raw egg on the table, and let it sit for several seconds.  Then, she gave the egg a gentle spin, and measured the time for it to come to rest.  We repeated this experiment for several trials with the raw egg.  Then, we repeated the experiment with a boiled egg.  Here are some data obtained for the two cases:

 Case Trial 1 Trial 2 Trial 3 Trial 4 Average raw egg 8 sec 7 sec 4 sec 4 sec 5.25 sec boiled egg 13 sec 14 sec 15 sec 12 sec 13.5 sec
Despite the fact that the two eggs have about the same mass, the raw egg dissipates energy of rotation more quickly than the boiled egg. There must be more "sloshing around" inside the raw egg, which uses up some of its energy, so that it will not remain in rotation for as long a time as the boiled egg.

26 April 2005: Terri Donatello [ST Edwards School]        Rolling Uphill  + Giveaways
Terry
brought in an apparatus that seemed to show an object rolling uphill. The object is a double cone (solid wood) that rolls on a pair of wooden rails, which are pitched slightly uphill as they widen. The cone seems to move ''uphill", because it rolls "up" the rails. It does so, because as the rails widen, the center of mass of the cone actually gets lower, as more of the cone falls below the level of the rails.

Terri then showed us how the "scratch test" is used to characterize the hardness of a mineral; this is one test used to identify an unknown mineral. Also, minerals will cleave in characteristic ways (depending on the forces that hold them together). For example, mica will cleave to form flat sheets ("isinglass"; see http://www.answers.com/topic/isinglass}, that were, at one time, used for windowpanes. The shapes of their crystals also are useful characteristics of minerals; NaCl, for example, forms a nice cubic crystal.

The Cell Game! This was a board game designed to teach the parts of a living cell, which Terri described as a "real treasure". And there were lots of other treasures that Terri brought that she has used to teach almost every area of science over the years. She offered them to the class members to take with them and use in their classrooms!

Terri, thanks for everything!

04 October 2005: Charlotte Wood-Harrington (Gwendolyn Brooks HS, physics)          Kinetics Problem
Charlotte
then talked about slopes and teaching slopes. Four volunteers each held a piece of PVC pipe about 8 cm in diameter that had been sliced in half lengthwise to produce troughs about 50 cm long. The team then was charged with producing a ramp that could roll a big super-ball into a tin can. This allowed the team to work together to adjust the slope of the four piece ramp to modify the speeds of the passage of the ball down the ramp. Eventually they got the ball into the can.  Neat ideas! Thanks, Charlotte.

01 November 2005: Terry Donatello (Weber HS, retired)            Distribution of Forces
Terry
also showed a demonstration of the "distribution of forces" (exercise 168 from the Giant Book of Science Experiments: http://www.amazon.com/Giant-Book-Science-Experiments-Press/dp/0806981393).  She used a piece of string wrapped around the hand. It is a principle that is important in understanding how pulleys work, in which a force can be distributed into equal half portions to two branches of a loop of rope or string.  She gave each of us a string, and we soon were testing the idea.  It worked!