1997-2006 Academic Years
Pressure and Density
16 September 1997: Larry Alofs [Kenwood HS]
Measuring the Density of a Gas
Equipment: Gas lighter, Graduated cylinder, Water tub, Electronic scale
Instead of measuring the mass of the graduated cylinder, he measured the mass of the lighter before and after expelling the gas into the graduated cylinder over-turned under water. The trick to good results is to have the lighter wet in both measurements...shaking off excess water before each measurement.
mass of lighter before (wet and shaken to remove water)
D = m/v D = .16g / 68ml = .0024 g/ml or 2.4 g/l
1 mole =22.4l (at STP) 2.4g/l times 22.4l = 54 g
After correcting for temperature it came to 59 g
The atomic weight of C4H10 is 58 grams/mole.
30 September 1997: 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 [0.01 kg] 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 .
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 * 0.121 m = .012 Joules .
P = 0.002 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.
Comments by Porter
10 March 1998 Larry Alofs [Kenwood Academy]
Re-designing a Boyle's Law [http://www.aquaholic.com/gasses/boyle1.htm] experiment without Mercury. Instead he is using ethylene glycol (antifreeze), along with a tire pump and a pressure/vacuum gauge. Thereby, he can achieve much higher pressures than would be possible with a Mercury column of modest height.
|Height of trapped air||Gauge Pressure||Total Pressure||P ´ V|
|5.6 cm||50 lb/in2||65 lb/in2||364 rel units|
|6.5 "||40 " "||55 " "||358 " "|
|8.1 "||29 " "||44 " "||356 " "|
|10.2 "||20 " "||35 " "||357 " "|
|14.2 "||10 " "||25 " "||355 " "|
|23.9 "||0 " "||15 " "||359 " "|
One must add atmospheric pressure to the gauge pressure to determine the total pressure P in the gas. Note that P ´ V is roughly constant as the gas volume is changed.
Another configuration with a thermal/ice water bath may be used to show Charles Law.
Earl Zwicker explained that a tire pump has a leather cup shaped seal, which is pushed up on the "up" stroke, and then on the "down" stroke it expands to provide a seal for the piston.
Porter Johnson: The most dangerous advice he ever received at a service station was that a low tire will "pump itself up" as you drive down the road, so that there is no need to pump up the tire. Actually, as the tire gets warm the pressure inside will increase, and an under-inflated tire will get dangerously warm because it is less rigid and there is more rolling friction. Heat, in turn, is the primary cause of tire failure.
Editor's Note -- Many gas stations have gone to the coin-operated compressors over a tank style—in part because people filling bicycle tires can be injured if the tire explodes when it is pumped to a ridiculously high pressure with a "tank" compressor
15 September 1998: Al Tobecksen [Richard Vocational HS]
He showed the bed of nails [ph8803.html] that he uses in class to calm troubled students and to teach pressure. Also, he showed that a flask of H2O with cardboard underneath usually doesn't spill when inverted. He "volunteered" an audience member and added some drama by switching from a small flask to a large one, using a parka to prevent the participant from getting soaked.
24 November 1998: SMILE: Ann Brandon [Joliet West HS]
She passed out a sheet of graph paper [old chart recorder paper, actually], and asked people to estimate the cross-sectional area of one shoe, in square inches. The people then weighed themselves [pounds], and calculated the pressure [standing on one foot and two feet] in pounds per square inch [lb/in2]. Most people obtained a number between 3 and 4 lb/in2 and it did not seem that the bigger people always had the higher numbers, since their feet were usually longer and wider also. The highest pressures are generated by people [primarily women] wearing "spike heels".
07 September 1999: Ann Brandon [Joliet West HS]
A Phyzz keeper
Old 2 liter bottles had smooth caps and occasionally pop off, sending the top flying with possible lawsuits, but the later bottles have a serration so that CO2 would be liberated with a swish, and not a pump or pop.
07 September 1999: Carl Martikean [Wallace HS, Gary]
[Given this equation for an ideal gas, the answers should be obvious, but to whom?]
He filled up a soda can and put a flame under it. Why does it boil when heated? When it reaches the vapor point then air is released, and some of it stays in the solution and creates bubbles. With the boiling water inside, the can is then tipped over into a tray of water, and the can collapses because the water vapor condenses and air pressure inside is reduced. Air pressure on the outside causes the can to collapse.
He also filled a test tube with water, raised the temperature till it boiled, capped the tube, and cooled the tube with a wet rag. The water under lower pressure as well as residual heat caused the liquid to continue boiling. Why? Boyle's Law.
Boyle obtained this law using a J-tube filled with mercury and heated to vary both pressure and temperature [http://members.aol.com/profchm/boyle.html and http://www.grc.nasa.gov/WWW/K-12/airplane/aboyle.html], which he also used to do the first investigations on Charles Law. Robert Boyle [1627-1691] argued against Aristotle's view of the four elements of earth, air, fire, and water; suggesting that matter was composed of corpuscles which themselves were differently built up of different configurations of primary particles. Boyle, whose work profoundly influenced Isaac Newton, was attacked by the Philosopher Thomas Hobbes for his ideas on the scientific approach. On Boyle's tombstone he is described as "Father of Chemistry and Uncle of the Earl of Cork". For details see the website http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Boyle.html
14 September 1999: Ann Brandon [Joliet West HS]
showed us a "ping pong ball cannon." A plastic water bottle (used by bicyclers) has an opening which accepts a ping pong ball with slight friction. Two nails had been poked through opposite sides of the bottle, near its bottom, to provide a spark gap within the bottle. Ann added a small amount of methanol, placed the ping pong ball into the bottle's mouth, and connected a piezoelectric spark generator (such as used to ignite propane stoves) to the nail electrode. When she triggered the spark generator - POW - the ball flew out across the room! (Not enough force to hurt anyone however.) Can you think of physics and chemistry concepts that are illustrated with this? Neat!
14 September 1999: Carol Zimmerman [Lane Tech HS]
set up a piston/cylinder arrangement made of glass, like a syringe. The piston (rubber) trapped air inside, and air volume V could be measured directly (in cc) on the glass cylinder. Weights (known masses) were added to the piston to compress the air to a smaller volume, and keeping a record of weight and corresponding volume, one could use the equation for pressure: p = mg/a, and test the relation between p and V. Since g and a (piston area) are fixed, and m is added mass (observed), p is directly proportional to m. From Boyle's law, pV = const, a plot of m vs V should show a hyperbolic relation. When we collected data, it did! Carol said that in the classroom, plots of p vs 1/V resulted in a convincing straight line. Nice!
04 December 2001:
Mary Scott (Williams School) Handout: Air Power
Mary used a small amount of air to lift a heavy load, to demonstrate the power of air. She inserted a drinking straw into a 4-liter (gallon) size "zip-lock" bag, and carefully sealed the opening with heavy-duty clear tape. She put the deflated bag on the table, and put a rather heavy book on top of it. When she inflated the bag through the straw, the book was lifted. She repeated the experiments with several books on the bag, demonstrating the effect of pressure of compressed air. The air blown into the bag becomes compressed, and exerts enough (additional) pressure to lift and then support the books.
Good work, Mary!
05 February 2002:
Barbara Pawela (May School; Retired and Still Enthusiastic) It's a Gas
For more details see her lesson on the SMILE website: chbi9916.htm
Barb continued with a description of the three states of matter --- (solid, liquid, and gas), and continued with experiments to study the behavior of air as a gas --- more precisely, as a mixture of gases.
05 September 2000 Carl Martikean (Wallace School, Gary, IN)
showed us 2 sharp pencils, 4 sheets of Cartesian graph paper, 1 tire pressure gauge, and asked - How can we weigh a car using this stuff?
Answer - drive the car with each one of the four tires standing on a sheet of the graph paper. Trace the footprint of the tire on the each paper. Use the gauge to measure the pressure in each tire. With the graph papers on the table, measure the areas of the footprints. The force on each of those footprints must equal the pressure in the tire multiplied by the area of the footprint. One must use the absolute or total air pressure in the tire, which is the pressure measured by the gauge plus atmospheric pressure. For example, if the pressure gauge reads 26 pounds/square inch, then we must add 14.7 pounds per square inch to 26, for an absolute pressure of 40.7 pounds per square inch. Multiply by the area of the footprint (suppose it is 30 square inches), and we have about 1200 pounds. If each of the 4 tires is identical, then the total force being held up (the weight of the car) is 4800 pounds! Thanks, Carl!
23 September 2003:
Therese Donatello [ST Edwards, Elmwood
+ Archimedes Principle
Terri led us through some simple experiments that are designed to help students take accurate measurements and write proper laboratory reports. [In her classes she asks students to develop and write a procedure for a laboratory experiment using part or all of the materials on a list that she provides.] She began by placing the following equipment and materials on the table:
Terri then asked us to determine the density of water using these materials (a simpler question), and we developed the following procedure:
A wonderful combination of ideas, Terri! Thanks.
07 October 2003: Porter Johnson [IIT,
Physics of Baseball
Porter asked the following questions concerning baseball:
04 November 2003: Gary Guzdziol [Carol Rosenberg Specialty
Drum Implosion Video
Gary showed us a video of the implosion of a 55 gallon drum, which was made at the SMILE summer picnic in Summer 1992. (Gary's father, Ed Guzdziol, did the experiment then.) Upon two separate occasions last semester [mp040803.html and mp042203.html], Gary heated a drum, but it did not implode, apparently because of minor leaks. In the video the drum creaked and made noises just before the implosion, and the sounds continued after its collapse. Why?
Gary stated that the drum was about 23 inches in diameter and 35 inches high. Thus, the total area of the two bases is about 835 square inches, and the area of the lateral surface is about 2527 square inches, corresponding to a total area of 3358 square inches. At a maximum pressure [inward] of 14.7 pounds per square inch, this corresponds to an total inward force of about 49,000 pounds. Wow!
Your video was dynamite, Gary! Thanks.
11 November 2003:
Christine Scott [Beethoven
School] FIVE SENSES --
FLOATING AND SINKING
Christine led us through a miniteach on the senses (focussed on vision) using the optical illusion phenomenon that occurs when a drawing of two objects about two inches apart are brought toward your eyes. FOLLOW-UP SUGGESTION: Try different separation distances (larger and smaller) and also note if there are peripheral images in each case.
We then had fun with floating and sinking. Well, we didn't actually either float or sink, but observed various objects doing so:
18 November 2003: Ann Brandon [Joliet West HS,
physics] Pressure, revisited
Ann described a project that she recently completed in her physics classes, in which students compute their pressure on the ground by measuring their weight W [with bathroom scales], and the cross-sectional area A of one of their feet using graph paper, in which the large squares are square inches. They make an outline of their feet on the graph paper to measure A. By taking the ratio P = W/A, her students obtained their "ground pressures", to be compared with air pressure of about 14.7 pounds per square inch. Ann then pointed out that airline stewardesses don't wear high-heeled shoes on the planes, because they tend to punch through the floor, causing a potential loss of cabin pressure. Spiked heels are made with a rubber pad glued onto a steel spike, which is attached into the heel. She also indicated that high-heeled shoes are a potential murder weapon. [Comment by Porter Johnson: see the film Single White Female starring Bridget Fonda and Jennifer Jason Leigh.] In the course of discussion, the following questions arose:
18 November 2003: Gary Guzdziol [Carol Rosenwald Specialty
Air Pressure Collapse
Gary put a small amount of water inside a clean metal one gallon can (about 4 liters), and with the cap off he placed it on a ring-stand. He heated the container with a propane torch for a few minutes, until the water inside began to boil. Then he turned off the torch, and tightened the lid on the can, wearing insulating cloves. The can began to make creaky noises as it cooled and contracted, and this process continued until the can had clearly collapsed in on itself. How come? The villain here, as with his large steel drum [mp110403.html], was air pressure. Next Gary showed a rubber pad about 3/8 inch (1 cm) thick, which he had obtained from a flooring store. He had cut the pad into a circle, about 10 inches [25 cm] in diameter, with a small hole punched through its center. He had pushed a string through the hole, and tied it to a small hard plastic ring a few cm in diameter. Holding the string, he dropped the rubber pad onto the floor. When Gary pulled up on the string, the pad stuck to the floor -- air pressure again. Gary was also able to pick up a fairly heavy table with the string when the pad was dropped onto it. He calculated the downward force of air pressure as the area of the pad (about 80 square inches) multiplied by air pressure (about 15 pounds per square inch) to be around 1200 pounds. Gary also showed us a rubber "dent puller", which can also be used for carrying large glass sheets, as well as presumably for climbing large buildings.
Gary also showed us that this collapse under air pressure has occurred on a larger scale with railroad cars that were sealed too quickly after steam cleaning. For details see the DR SLIME website: The Can Crush Demo with a Real Life Example: http://www.delta.edu/slime/cancrush.html.
Very dynamic and interesting, Gary! Thanks.
02 December 2003:
Ann Parham and Winifred Malvin [Carver Elementary
Ann and Winifred started by mixing about 25 mL of liquid detergent with about l Liter of water, inside a clear plastic container. They then used the sudsy water to make bubbles, which we used to illustrate and study Bernoulli's Law. Some details are given by the article Bubbularium (make an observatory to see the amazing colors in bubbles) http://www.exploratorium.edu/science_explorer/bub_dome.html, at the S. F. Exploratorium website. In addition, activities are described on the Bubble-ology & Bernoulli website [http://www.scoe.org/content.php?PageId=208]
Winifred briefly talked about Bernoulli's Principle and its relation to flight, and we did some activities in bubble-ology. We divided into groups of 3-4, which began to conjure up and investigate strategies for keeping a bubble in the air. Each group had about 100 mL of sudsy water as well as a straw, and we went to work! Carol Giles found that it was very effective to fan the air above the bubble with a sheet of paper. Why does that work? Should we ask Bernoulli?
Winifred and Ann then followed the instructions in the Bubbelarium article, making and studying fantastic bubbles. We saw great images and rainbows in the bubbles. How come?
Just sensational! Thanks.
02 December 2003:
Joyce Bordelon [Moos Elementary
and Glider Construction
Joyce gave us information and templates obtained from the article entitled 757 Glider Kit (in pdf format) http://www.nasa.gov/audience/foreducators/topnav/materials/listbytype/757.Glider.Kit.html, which is located on the NASA Spacelink Educational Materials website: http://www.nasa.gov/audience/foreducators/topnav/materials/about/index.html. We then proceeded with a very successful launch of gliders, using the information obtained there.
The gliders were a big hit! Great, Joyce.
02 December 2003:
Barbara Pawela [May School,
Surface Tension of Water: Handout
Barbara led us through a miniteach that she developed in the Summer 1995 SMILE Program: ch9510.html. The activities involved a study of adhesion, cohesion, molecular attraction, and surface tension --- as well as their role in detergents and other cleaning agents.
We love these classic lessons; they are timeless and relevant --- and lots of fun! (just like the reruns of I Love Lucy©) Thanks Barbara!
02 December 2003:
Marva Anyanwu [Wendell Green Elementary
School] Surface Tension of
Marva introduced still more exercises on surface tension, which we will finish next week. We began by dividing into groups, with each group being given about 65 mL of milk in a Styrofoam plate. We investigated phenomena associated with mixing, using food coloring (three different colors) as well as liquid detergent. Each group developed its own approach to investigating the matter --- hypotheses, expected results, procedures, conclusions. Swirls of color were formed when the colored drops were dropped into the milk. New colors were formed when two regions of two different color were stirred together. When a droplet of detergent was added to a region of a given color, the color change propagated from the location of the droplet outward. As described in the previous miniteach, this propagation by diffusion occurs because of the surface tension of the water--- the primary ingredient of milk. It was especially impressive to watch the propagation, because it was so easy to see the colors change.
09 December 2003:
Marva Anyanwu [Wendell Green Elementary
School] Surface Tension of
Marva passed around information on Surface Tension obtained from the GSU HyperPhysics websites [http://hyperphysics.phy-astr.gsu.edu/hbase/surten.html and http://hyperphysics.phy-astr.gsu.edu/hbase/surten2.html]. In particular, there were paragraphs on Surface Tension and Bubbles, Bubble Pressure, Surface Tension of Water, and Cohesion and Adhesion She also passed around information from the website (German) Messtechnik GmbH® [http://www.online-tensiometer.com/], concerning Surface Tension Experiments [http://physics.about.com/od/physicsexperiments/a/surfacetension_4.htm], including Water Hill and The Strength of Soap. We continued the study of bubbles from the last SMILE meeting [bc120203.html], and discussed their meaning. We learned that the pressure inside a bubble is slightly greater than outside atmospheric pressure, because of the effect of surface tension to produce a "wall tension". Also, bubbles assume spherical shapes to minimize that "wall tension". The result also applies when a bubble is surrounded by a liquid, such as in the alveoli of the lungs. The properties of cell membranes determine the shape of cells inside living organisms, for similar reasons. Thanks Marva! Quite interesting.
12 October 2004:
Marva Anyanwu [Wendell Green Elementary
Sinking a straw (Handout)
Problem: Determine the number of BBs necessary to sink a straw to any chosen depth in water.
Materials: sinking straws, BBs (#9 lead shot), metric ruler, beaker, water, small rubber band, modeling clay (for plugging straw)
We carried out this exercise in class with enthusiasm, obtaining good results. Thanks for sharing this, Marva!
23 November 2004: Don Kanner [Lane Tech HS,
Don first showed us how to get Helium balloons off the ceiling of a room, using a 2 meter stick with double-sided masking tape wrapped around it. In addition, he showed how to do the same thing using ordinary masking tape -- just wrap the tape around an end of the stick, giving it a twist so that some of the sticky side would be outward. Very useful tricks with a clever twist, Don!
Don went on to measure the time for a Mylar® balloon filled with Helium gas to rise H = 2 meters to the ceiling, when released from rest. The time was measured to be t = 2.7 seconds. If we assume that the motion corresponded to a uniform acceleration, that acceleration is
Don finished by taking several breaths from the Helium balloon, after which he said -- in a high-pitched "Helium voice" -- the very familiar-sounding words: Tha- tha- thats all, folks! Fascinating, Don!