High School Physics SMILE Class
30 September 1997
Notes taken by Porter Johnson
First, some important
information on
obtaining science materials.
- The
American Science Center has a new store in the Orland Park
mall. The address is 15100 S. Lagrange Avenue.
- There
will be an ISPP meeting on Thursday 16 October from 6:30 - 8:30
pm in Joliet West High School, hosted by Ann Brandon and Deborah
Lojkutz.
- Ernest
the Dancing Bear can be
obtained for $20.00 at a store called ALL WOUND UP, located in
Gurnee Mills near the Rain Forest Restaurant. TEL: [847]
856-1208.
- Euler’s
Disk is available at the store Yes, World of Science in the
Chicago Ridge Mall at 95th Street and Ridgeland Avenue.
******
Karlene (Kurth) Joseph announced that there would be a
temporary position
for a Physics teacher at Lane Tech High School for a period of about 7
weeks,
during which she would be on leave.
The first presentation was made
by John
Bozovsky of Bowen High School, 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 b y 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 judgement of the group that the
dev ice
needed a longer arm, a shorter span, and a faster motor, and there was
elaborate discussion of these points.
The next presentation was by
Walter
McDonald [CPS Substitute teacher and worker in VA hospitals] of a
device to
measure lung volume and the pressure generated by strong exhalation.
He was able to expel a volume of
about 2.5
liters from his lungs in a single breath, as measured by the device.
In the process of exhaling, he
was able to
lift a 10 gram [0.01kg] mass sitting on a light platform inside a
cylinder to a
height of 12.1 cm. The radius of the cylinder was r = 2.5 cm,
corresponding to
an area
A = p r 2
= .002 meters2 .
The force exerted by exhaling is
equal to
F = m
g = 0.01
kg * 9.8 m/sec2 = 0.1 Newtons .
The < average, excess> air
pressure
exerted by the lungs is thus
D
P = F/A = 0.1 Nt / .002 m2 = 50 Nt/m2 [Pascals].
This pressure is a small
fraction of
atmospheric pressure,
PA » 100,000
Pascals ,
indicating that in exhaling [or
inhaling]
the pressure is very close to atmospheric. This fact is understood by
snorkelers around the world, who know that one cannot "snorkel" [auf
Deutsch "schnörkel" = "spiral"] at a depth or more than
25-50 cm.
The process of exhalation took
about 6
seconds. The work done in lifting the mass to that height was
W = m
g h = 0.01
kg * 9.8 m/s2 * .121 m = .012 Joules .
The <average> Power is
obtained by
dividing this work done by the time of 6 seconds, corresponding to
P =
0.01 Watts .
There was some discussion of the
use of
computers in the classroom, and it was felt to be a good idea, so long
as you
are sure that the students understand the "big picture" of what is
happening.
The next presentation was made
by James
Chichester of Lincoln Way High School, who handed out a Bound
and Gagged
cartoon of a dog hanging his
head out of a
car. When the car stopped suddenly, the dog seemed to move backward in
his seat
[even though the wretch did not appear to have a seat belt on], and
ended up
with wrinkles in his bottom half. Clearly, the author of this strip
[who also
did the escalator cartoon shown last year in SMILE] has a non-Newtonian
perspective on Physics.
Alex Junievicz [CPS Substitute Teacher] did a
demonstration
involving a "cow magnet" [used by farmers to remove metallic objects
from cow stomachs] dropped down tubes that had inside diameters a
little larger
than the diameter of the [ roughly cylindrical] magnet. He showed that
the
magnet fell quite freely inside a plastic [PVC] pipe, whereas for a
copper pipe
it was slowed down [presumably by eddy currents], even though the
copper
pipe had a longitudinal strip removed from it. The magnet fell
quite freely
through an aluminum pipe of somewhat larger diameter, however. The Al
pipe [scrounged
from the shop the Lee Slick] was very short and thin, and the eddy
currents may
not have been set up well in it. The definitive experime nt would
require a
solid copper pipe, and an Al pipe with thick walls.
There was subsequent discussion
of the
book Conceptual Physics by Paul Hewitt. It was suggest
that the
book would be appealing to students who understand the concepts of
mathematics,
but who do not like quantitative problems. However, i t may not be
suitable for
students who neither like nor understand mathematics [i.e. algebra].
Fred Schaal [Lane Tech HS] raised the question of
whether
NASA tapes of the moon landing
could be
used to prove/disprove to skeptics that the moon had no atmosphere and
reduced
gravity. For instance, during the filming of the take-off of the lunar
module,
is it evident from the dust pattern that they were on the moon? Porter
Johnson suggested that the best evidence might come from a study of
the
trajectory of the golf ball, which should be truly parabolic on the
moon, with
no possibilities of a slice, no effect of back-spin, etc. Air
resistance is v
ery important for the flight of a golf ball on earth, in contrast to on
the
moon.
Ann Brandon [Joliet West HS] demonstrated the use
of the Trundle
Wheel to measure distances, and she tried it out on the carpet in
118 SH.
She laid out a distance of 2 meters with meter sticks. When she went North,
the distance r ead 1.985 m, whereas going South it read 2.010
m.
Similarly, going East she obtained 2.02 m, versus 1.985 m going
West.
How come? The answer seems to relate to an asymmetry in the nap of the
carpet.
As a test, the distance going < B>SouthEast was 2.01 m, whereas
going NorthWest
it was 1.99 m [I think!]. Verrrry interesting!!
Porter Johnson did a demonstration of using the points
on ae
compass to specify directions using a real compass to
interested parties
after the class.
Addendum to Smile Notes of 30
September
1997: Alex Junievicz
Ernest the Dancing Bear
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 th at 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
1. Stretched string sagged --
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
------------------------------------------------------------
Walter Mcdonald
Walter brought in a medical
apparatus for
measuring lung capacity.
Comments by Porter
The volume of the lungs is an
excellent
indication of a person’s health. A balloon or this type of apparatus
helps the
medical people determine the condition of a person’s lungs.
The power output of the lungs is
in the
area of 2milliwatts, whereas on a bicycle the power of a cyclist may be
of
order of 100 w, but it is difficult to maintain that level of power for
very
long.
The results should be rounded to
not more
than two significant place, and possibly on to make the statistics easy
to
interpret.
Alex Junievicz
First a comment on the Train
commercial.
Running full blast then stopping is a way of getting maximum gas
economy on a
car. [allegedly!!] The engine is at maximum efficiency at High output,
thus
accelerating and coasting and accelerating. and coas ting is a bad way
to
drive, but gets better gas mileage.
For my presentation I brought
two pipes,
on of PCV [plastic conduit], and a Copper tube. Taking a cow magnet and
dropping down the two pipes showed that the magnet induced a field in
the pipe
that eventually slowed the magnet down. Cow magnets ar e not digested
when in
cows [four] stomachs, but they do catch metal objects, filings, barbed
wire,
etc in the 1st Stomach of a cow preventing damage further on. The
magnet I got
from Farm and Fleet in Wisconsin. has 5 smaller magnets and is about 3
cm l ong
and about « inch diameter. Thus tubing with a « inch ID will work. I
used a 4ft
piece of pipe ($4.20 for the Cu and $1.40 for 10 ft of PVC conduit; the
cow
magnets were approximately $2 each in packets of 3)
I was very surprised that, when
I cut the
tubing lengthwise, there was little change I expected breaking the
short
winding that there would be little effect on the magnet. There was less
Cu ,and
I suspect that was the main reason for the faster travel
As the birdies go "Cheep -
Cheep" as I am walking around, I haven't been able to find any
appropriate
Aluminum Pipe - Note: Iron/Steel will not work as the magnet
sticks to
the pipe and does not slide.
Late Bulletin from Alex:
The reason for this note is that
Al does
slow the magnet,. but not as much as Cu. I am having a hard time
finding a
suitable Al tube.
Also made a comment about
Hewitt's book.
His claim was to make understanding the key and not problems. Attending
his
workshop I felt his use of formulas as a guide to understanding no
consistent
with some of the students that had no math competence. He expected if
you say
the formula A=C/D that the student would realize that if D goes up then
A would
drop. I found that giving all the permutations of the formula and then
plugging
in allowed more student to do problems (helping with a way to choose f
ormulas
and gain some self esteem). I agree that competent students can use
formulas, but at this point
trying the get
the Physics first.
Fred Schaal Lane Tech
Fred commented on the there was
an option
that the Moon Walk -etc was a fake. The trajectories ware not
appropriate for a
vacuum. It was pointed out that there were other views on tape that
showed the
actions better than the ones on the news.
The trajectory of a ball on
earth---with
wind resistance---and on the moon are quite different. The section of
ellipse
that would show what happens on the moon is shorted on the earth. An
800 foot
home run would become 400 on earth. Porter suggested that a ball hit in
Denver
will travel further than one hit at Boston (sea level). In soccer the
term
"Banana Kick" is used to describe the altered path. Also in golf the
dimples cause turbulence and make the ball go further.