High School Physics SMILE

28 April 1998

Notes taken by Porter Johnson

1. Summer 1998 Program: 06-31 July 1998; 1:15 - 4:15 pm. To sign up, contact

Porter Johnson at 1-312-5675745.

2. Our write-ups for high school physics classes during the 1997-98 can be viewed

or down-loaded from our web page: http://www.iit.edu/~smile/

As part of the joys on retirement, Bill showed us his elegant and functional new Bush Pruner with recessed head [available at Sam’s club for circa $20] and Fiskars pruning scissors [circa $12] with offset handles.

Bill then described his quest to make an LED flashlight. The LED devices require 2.2-2.7 Volts to fire [for sufficient energy to overcome contact potentials and to produce photons], and thus will not work with 1.5 Volt flashlight batteries. However, with 3 Volt Lithium Cells [available cheap at Walgreens and, no doubt elsewhere] he was made a light. The LED itself has a short lead [-] and a long lead [+], and on the inside the [-] side is connected to a large electrode, whereas the [+] side has a small electrode inside. The Li battery must be used in connection with a "ballast" resistor, since 3 Volts will lead to "thermal runaway" and breakdown---although the latter point is mollified somewhat by internal resistance of the Li battery. [small batteries have fairly high internal resistance]. He also had a Blue LED that operates with a 6 Volt battery.

Comment by Porter Johnson: The Planck Formula E = h n = h c / l can be switched to practical units by using the relation

h c = 1238 electron Volt · nanometers [eV· nm].

Thus, the wavelength l [nanometers] corresponds a battery voltage V [Volts]; V = 1238/l

Light Color Wavelength [nm] Voltage[Volts]

Red 700 1.8

Orange 600 2.1

Green 500 2.5

Violet 400 3.1

He brought in a long piece of wood trim [rectangular cross-section, with thick and thin sides] with a DC motor attached to one end, which was driven at various rotational rates by varying the input voltage. At lower speeds [frequencies] he obtained the resonances for "transverse vibration" of the rod [motion in the direction of thin side], which was clamped to the at the other end. With higher frequencies he obtained the "longitudinal vibration" of the rod [motion in direction of thick side]. Arlyn also have a "mechanical resonance" device for measuring the frequency of vibration by looking at the resonant motion of one of the internal masses.

He said that this system [and many other ones] have the property known as a "tipped resonance curve", in that the resonance amplification factor [gain] is asymmetric with respect to increasing and decreasing frequencies. He said that such a property arises because of non-linearities in the mechanical system, according to one of his instructors.

Chris described a project in her school of raising butterflies from larvae, and observing their metamorphosis from the caterpillar [pupa] stage into full adulthood within a few weeks. There is a fairly large enclosed region [about 2 meters on a side] in her classroom.

One may order the butterfly larvae from the following supply house:

Ever attentive to scatology, Fred Schaal asked for the word for butterfly droppings [frass, from German fressen = devour]. Comments by Porter Johnson:

[1] the word for "butterfly" is strikingly different in many closely related languages:

vlinder Dutch

papillon French

flinter Frisian

Schmetterling German

p e t a l o u d a (petalouda) Greek

farfalla Italian

papillo Latin

lepke Magyar [Hungarian]

motyl Polish

babochka Russian

mariposa Spanish

fjäril Swedish

[2] Speaking of scatology, the English word "butterfly" is of uncertain origin, but may refer to the "buttery" character of the droppings [according to OED, there is an Old Dutch word "boterschijte"].

Fred asked why slugs leave a trail of material [slime] when they cross the tennis courts, and why that trail is thicker in some spots than in other. The answer is that the leave as much slime as they must in order to proceed, and if their travel becomes more sluggish [so to speak] they leave more slime. Also, slugs respond to certain chemicals [NaCl: salt] by producing more slime.

Barbara played segments of Latin, Rap, Rock, and Classical Music [each a few minutes long], and we used skin temperature devices [described by hawkers as "mood indicators"]

to determine our psychic state while the music was being played. Most of us were either "calm" or "normal" during the Latin and Classical sections, and somewhat "tense" or "under tension" during Rap and Rock sections. [Comment by PJ: the classical piece, Einekleinenachtmusik by Mozart, was quite rousing].

She showed posters in which 8^th Grade science students had been assigned a chemical Element, and had prepared a report and poster on that element. The elements mentioned were Gallium [Ga], Phosphorus [P], Barium [Ba], Silver [Ag], and Copper [Cu].

Comment by PJ: There is an excellent book on the elements:

The Elements

John Emsley

[Oxford 1991] 2^nd Edition

[paperback] ISBN 0-19-855568-7

She spoke about the meaning of the word "physic": a medicine or remedy, especially a laxative or cathartic which is completely different from the meaning of "physics": science dealing with the properties , changes, interaction, etc of matter and energy. The two words do come from the same Greek root [f u s i k a (physica) = nature].

Also, she spoke of folk remedies for colds and fever, such as the oat and bread water, citrus fruits, and the famous sassafras tea.

Comments by Porter Johnson: while you are within your constitutional rights in waiving immunization for childhood diseases, it is not a good idea to avoid them, or to try to treat serious diseases [Hepatitis C, Meningitis, Mumps etc] with folk remedies. Also, I read recently in Discover Magazine that half of the people who have ever been born died of Malaria—most before the age of 5. Modern standards of sanitation, refrigeration, transport and storage of food, and agricultural technology are probably as important as medical miracles in increasing the average lifespan.

Have a good summer. See you next fall!!