Mathematics-Physics HS SMILE Meeting
7 December 1999
Notes Prepared by Earl Zwicker

Porter Johnson (IIT) put us to work cutting out a paper pattern to construct an icosahedron. When some of us had completed it, we had what could pass for a nifty and science-based Christmas tree ornament. Porter gave us a website where we could read the hs physics write-ups for the last 3 years on the web. http://www.iit.edu/~smile, and in his inimitable style gave us mathematical and other insights into this shape. Thanks, Porter!

Carl Martikean (Wallace School, Gary)

described how to make a 2 liter pop bottle stomp rocket. See the website http://www.sciencetoymaker.org/airRocket/index.html ... and someone remarked that the active ingredient [energy source] for this device is your foot!

Bill Colson (Morgan Park HS)

read some excerpts from Education Week, Nov 24, 1999, Setting the Record Straight, http://www.edweek.org/ew/vol-19/13thiswk.htm pointing out the frequent misconceptions people have about---for example---our solar system. See http://www.ems.psu.edu/~fraser/BadScience.html. When answering the question: Why is earth hotter in summmer and colder in winter? -- people would usually state that earth was closer to the sun in summer and farther away in winter. Of course, the opposite is true. And what about the southern latitudes!? Interesting stuff, and reminding us of the frequent indifference people have for things scientific/technical. We have our work cut out for us!

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!

As our meeting progressed, several physics teachers and their students joined us. They were here for the special lecture on Bridge Building, to gain insight on constructing a strong bridge. (The Chicago Regional Bridge Building Contest will be held on Tuesday, 15 February 2000, as one of our regular SMILE meetings in math-physics.)

Eduardo De Santiago, Assistant Professor in IIT's Department of Civil and Architectural Engineering

introduced himself and explained that structural engineers design not only bridges, but are involved in design of nearly all structures: buildings, space platforms, dams, ships, antennas,... He soon had us involved in answering questions.

• What is a bridge?
• How would you define it?
• What is its function?
Dialogue established that a bridge provided a way for things (traffic, people, etc) to move across a chasm, river, etc. Consider a simple bridge: a plank supported at each end. If a load (person) stands at its center, what happens? A student provided an answer: It bends. And so it went. With a few sketches, Prof De Santiago soon had us considering bending moments (M) and shear forces (V) - both internal forces - and how they affect the plank. We defined internal stress from a sketch of the distribution of forces across a section of the plank, with the NA (neutral axis) on the geometric axis.

In less than an hour of give-and-take, he led us to develop an intuition for the factors that affect the strength of structures, and to the truss bridge. We came to understand these terms: floor beam, panel, bottom and top chords, portal bracing, internal bracing.

Along the way, the Chief Judge for the Contest, Mr George Krupa, who is involved in the structural engineering of bridges, fielded still other questions.

Three tips offered by Prof. De Santiago:

1. maintain symmetry
2. minimize the number of connections or joints
3. craftsmanship is very important

What a wonderful evening!
HAPPY HOLIDAYS!
SEE YOU IN THE NEXT CENTURY!!