ISPP REMINDER
September 2010
OUR NEXT MEETING. . .
. . . is at Oak Park- River Forest High School
Wednesday
October 20, 2010
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!
FUTURE MEETINGS. . .
Dec 7 (Tuesday) DePaul University – John Milton, Andy Morrison
Jan 19 (Wednesday) Elmhurst College 27th Annual "Tri-Physics" Meeting – Earl Swallow
OTHER MEETINGS . . .
Nov 20 (Saturday) ISPP-CSAAPT-PSAPS at IIT, Chicago
Jan 8 -12 (Wed - Sat) AAPT National Meeting, Jacksonville, FLA
AT OUR LAST MEETING. . . .
Debby Lojkuta (Joliet West High School) opened
the meeting by introducing the Joliet teachers: Arthur Glaser, Joliet West, Zak Knott and Rich Goberville of Joliet Central. Then Debby
started with a phenomenon and asked for volunteers to help. She had one of us
sit on an Arbor Scientific Human Dynamics Cart ($159) (a skateboard will
suffice) while holding on to a handle with a rope attached. The rope was hooked
onto one end of a spring scale. The other end had a second rope with which
another of us attempted to pull the cart with a constant force, as indicated on
a spring scale. After a few false starts, and learning to overcome the initial
inertia, they were able to keep the reading pretty constant at 15 Newtons. She
timed how long it took to move a fixed distance. We got a sense of how fast the
cart was accelerated with this force. Then Debbie instructed us to double the
force to 30 Newtons, and she again timed how long to move the same distance. We
ran a trial using three times the force. For each trial the time got shorter
with increased force. Then Debbie added another person to the cart. Debbie
explained that she has enough carts for four groups operating in the hallway in
different directions. She handed out copies of the exercise sheet the students
fill out in doing the Lab. What a neat way to get students involved in the
experiment.
Gordon Ramsey (Loyola University) announced the summer AP workshop dates, July 11 – 15 at Loyola. He suggested we ask him or Martha Lietz (Niles West High School) for more information.
We asked for new teachers to be
recognized. Jared Maraska stood up and received a New Teacher’s Bag
John Milton (DePaul University) updated us about Gerry Lietz’s health and we all wished him well. He pointed out up and coming meetings. Andy Morrison (DePaul) added that the AAPT Chicago meeting at IIT will feature the new Prairie Section of APS and will have an interesting keynote speaker Steve Lid (sp) from Trane Air Conditioning Co. and member of the Standards Committee of the Acoustical Society of America. He will be presenting ideas about lab activities for high school and college classes.
Roy Coleman (retired CPS) heard from Ed McNeil, one of our founding fathers, now living in Montana. At 89 he is “hanging in there”. Ed had noticed an interesting physiological phenomenon in color perception while assembling jigsaw puzzles. At first glance two pieces might look like they should match by their shapes but the colors don’t quite match. When the pieces are place together the hues appear to shift so that they do match by color too. The effect is consistent with Land’s theory of color perception across boundaries. Glad to see Ed is still thinking about physics. Roy also heard from Janet Landato.
Marcel Chiu (Rockford East High School) lamented that he has one physics class of 14 students and next year the school is posturing to eliminate classes having less than 25 students. He hopes, as do we, this will be a year of building enrollment. Marcel welcomes any suggestions. He just picked up some TI motion detectors and is excited about using them this year. He had replaced a teacher who was there for 14 years.
Marcel recently coached a group of students participating in the Rockford area Science Olympiad. Marcel explained the structure of the competition and showed some pictures of his students participating.
Martha Lietz (Niles West High School) set up an
incline cart track and mounted a cart with a plastic sail to use with a motion
detector and Vernier Data Logger to track the motion of the cart. Martha had
just done this recently in class as a demonstration and stirred up quite a
controversy among her students. She told us she was going to let the cart roll
down the incline and asked us to predict the velocity and acceleration plots
with the motion detector at the top of the ramp and the cart at the top moving
away. We made our guesses and then she let the cart roll down and the software
produced the corresponding plots. She tried using different arrangements of the
incline and sensor. Instead of asking her students to check their answers with
their fellow students, Martha found the approach used by Eric Masur, to have
the students find an answer different from theirs, to be a better strategy. The
arguments came for the case of the cart going up the ramp towards the detector.
Can deceleration ever be positive?
Art Schmidt (Northwestern University)
positioned a vertical front surface mirror in the back of the room. He aimed a
green laser pointer from the front of the room to reflect off the mirror so
that it returned to the front of the room hitting the projection screen. He
noted that the spot was just a smear of light with no structure. Then he
covered the mirror with a small aperture. The splotch of laser light now
displayed a bulls eye interference pattern with regularly spaced concentric
rings of light. We had to go up close to the screen to be able to see the
pattern over the glare of the laser light. Art asked us what we thought was the
source of interference. We mostly agreed that what we were seeing was the
interference due to the finite size of the aperture and that the mirror only
turned the light back toward the source. Then, Art brought the mirror and
aperture close to the laser and used a small double concave lens to create a
divergent beam. Oddly there was still an observable structure in the beam
reflected off the mirror aperture arrangement. The pattern of interference
rings was not regularly spaced as before but became finer toward the center.
Gordon Ramsey suggested that the difference be in the closeness of the
geometry. For long distances we use Fraunhaufer geometry but for short
distances Fresnel geometry.
Roy Coleman (retired CPS) had a few ideas for Modern Physics experiments. He found that beading cubes (a cube with a hole drilled through) available at Michael’s or some other craft store, a thousand @ $40, work nice for demonstrating radioactive decay. Throw down a given number of cubes and remove any that land with the hole up. Roy claims to have measured a decay constant of ‘not quite’ one third. The exercise can be completed in a single 50-minute class. Having a die with one side painted black can be used to show mother-daughter decay. After throwing the beading blocks, replace any hole-up block with a die. Throw the surviving bunch again, replace ‘decayed’ beading blocks with painted die and remove any dice with black side up. Repeat again and again. The number of dice should grow and then diminish with a decay constant of one sixth. This one might need a double period. Neat!
Then Roy described his version of the Rutherford Experiment. He calls it ‘the size of a monster’. He passed out a sheet describing the exercise. He places an object (the monster) in a large box and has students roll marbles, one at a time, into the box randomly directed. They keep track of the times the marble hits or misses the monster. Knowing how large the marble is compared to the total width of the opening, one can determine the linear width of the monster without ever seeing it. To spark their imagination he tells them that when they hit the monster, it growls (more like a clink) and then it moves to a new location.
Art Glaser (Joliet West High School) explained that there is a lot of examples of Physics (and Chemistry and Biology in the human body. The semicircular canals of the inner ear to show inertia of fluid flow in balance, pulley’s in the tendons that go over the kneecap, levers in attachment of muscles and limbs.
Bill Blunk (retired Joliet West High School)
recalled the many years of bridge building contests and trophies awarded to the
winning school accumulating in hall cabinets. Debbie recently found the first
annual national bridge building contest trophy from 1978 awarded to Craig
Randolph. Craig’s bridge was the only one over the years that was not broken,
for lack of enough weights on hand. Bill went through a box of old bridges in
his basement and found Craig’s unbroken bridge, which he returned to Craig. Now
he can also give him the trophy that went with the bridge. Craig was
overwhelmed to be sure.
Debby Logkutz (Joliet West High School) announced our free giveaway that was a reworking of an exercise involving vectors introduced by Jim Szeszol using Popsicle sticks. Debby handed out a copy of the exercise along with bags of whole Popsicle sticks and ones cut in half. Each was labeled with an angle of direction. The instructions guide the students to graphically sum six vectors by laying then out sequentially head to tail and specifically noting the starting and ending points. The students are directed to mix the sequence of adding vectors. By noting the near identical starting and ending points they learn that summing vectors is commutative. Submitted by Art Schmidt
Art Schmidt (Northwestern University) has been making videos of meetings and now has made them available on the web. The Joliet West meeting is viewable at http://wildcat.phys.northwestern.edu/public_html/ISPP%20Joliet%20West%20HS%202010.mov
For info about ISPP go to http://ispp.info.com or http://ispp.slinkset.com/
Directions to Oak Park – River Forest High School
From points South — Take I-94 Dan Ryan downtown. Exit to I-294 Eisenhower (west). Exit at S Austin, Turn north on Austin to Lake. Turn left on Lake to Scoville. Park on the street around the school. Look for ISPP signs at the school entrance which is located on Scoville Ave. at the approximate center of the building.
From points North — Take I-94 Edens south. Merge
with the Kennedy. Exit to I-294 Eisenhower Exit at S Austin, Turn north on
Austin to Lake. Turn left on Lake to Scoville. Park on the street around the
school. Look for ISPP signs at the school entrance which is located on Scoville
Ave. at the approximate center of the building.
Mother – Daughter Radioactive Decay
Name___________________________ Name__________________________
Name___________________________ Name__________________________
Total 'Holes' (beading cubes) at start=____________ (S)
Throw 'Holes' 'Holes' Dice Dice Dice Dice
Number Removed Remaining Before Added Removed After
1 | (B1) |(S)-(B1)=(HR1) | 0 | (B1) | 0 | (DA1)=(B1)
--------+----------+------------+--------+--------+-------+-------
2 | (B2) |(HR1)-(B2)=(HR2) | (DA1) | (B2) | (DR1) |(DA1)+(B2)-(DR1)=(DA2)
--------+----------+------------+--------+--------+-------+-------
3 | (B3) |(HR2)-(B3)=(HR3) | (DA2) | (B3) | (DR2) |(DA2)+(B3)-(DR2)=(DA3) --------+----------+------------+--------+--------+-------+-------
4 | | | | | |
--------+----------+------------+--------+--------+-------+-------
5 | | | | | |
--------+----------+------------+--------+--------+-------+-------
6 | | | | | |
--------+----------+------------+--------+--------+-------+-------
Etc.
THE SIZE OF A MONSTER
You are approaching a dark room which contains an immortal monster. Your job is to find out how wide this monster is without entering the room (and taking a chance on being eaten).
There is a thin slit across the entire width of the room but the room is so dark that you cannot see into it even with a good light. You can, however, throw rocks into the room. Whenever you hit the monster with a rock it makes a loud growl (it actually sounds more like a 'klink') and then moves to a new location but never touching the walls.
To get enough valid data, your group needs to randomly throw at least 200 rocks. You will need to keep track of how many rocks you throw through the slit and how many actually hit the monster.
1) From this information you should be able to write down the ‘uncorrected’ width of the monster. (HINT: If the monster were half the width of the room, what percentage of the randomly thrown rocks would hit it?)
2) Unfortunately the answer to #1 assumes that the rocks are infinitely small. What is the width of the monster corrected for the size of the rocks verses the size of the room? (HINT: If the room were 100 units across, the rocks were 10 units in diameter and the monster 91 units wide, what percent of the throws would hit it?)
3) Finally, the answer to #2 still assumes that the rocks are infinitely small relative to the monster. What is the final corrected width of the monster after correcting both the room size and the monster size for the size of the rock?
In each of the previous parts you should do an error analysis and determine both the actual error and the acceptable error. Your write-up should include a data section, three sample calculation sections, three error analysis sections and a conclusion.
This experiment is due today at the end of the period (assuming a 50-55 minute period).
Your group will lose 1 point for each rock that you do not return at the end of the class period.
