High School Physics SMILE Class
30 September 1997
Notes taken by Porter Johnson
First, some important information on obtaining science materials.
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.
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 bearís pants.
- The setup that failed-The arm on the motor was about 10cm long
1. Stretched string--need stronger stuff
2. The arm should be longer
3. Drag on the pulley
The pulley on the road being lifted and dropped is to move the toy on the pulley
Walter brought in a medical apparatus for measuring lung capacity.
Comments by Porter
The volume of the lungs is an excellent indication of a personís health. A balloon or this type of apparatus helps the medical people determine the condition of a personís 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.
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 ę inch diameter. Thus tubing with a ę 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.