Karlene Joseph (Lane Tech HS) Gas Laws
Karlene handed out two flasks (round bottom Florence flasks, 500 ml). Each flask contained 50-100 ml of water, with a partially inflated balloon inside. Karlene asked us to explain how she got these balloons inside the flasks, and why they would remain there. There were suggestions that the procedure for implantation of the balloons inside the flask might involve some sort of heating. At this point she reviewed the gas laws:
|Charles Law||Volume / Temperature = Constant||Fixed Pressure|
|Boyle's Law||Pressure ´ Volume = Constant||Fixed Temperature|
|Gay-Lussac's Law||Pressure / Temperature = Constant||Fixed Volume|
|Ideal Gas Law||Pressure ´ Volume / Temperature = Constant||General|
Karlene then set up the apparatus, and we learned how to get the balloon inside the flask. She began by partially filling the flask with water, and heating it to boiling on a hot plate. The air inside the flask was largely replaced by steam in this process. After removing the flask from the hot plate, she quickly inserted an unfilled balloon into the flask, attaching its open end around the "lip" of the flask, so the un-inflated balloon lay along and inside the top neck of the flask. As the flask cooled and steam condensed, the gas pressure inside the flask became less than air pressure outside, and the balloon began to inflate inside the flask. The whole process took a few minutes.
At the suggestion of visitor Fred Schaal, we then heated the flask (with the balloon already inflated inside it), and again we produced steam from water. The net effect was that the balloon became everted, and it even inflated a bit outside the flask. When we cooled the flask again, the balloon was pulled back inside the flask and filled with air. Note: Here is the description of a very similar experiment:
Balloon in a Bottle:
"A 300 ml florence flask ...[*** a thin-walled pyrex vessel] ... can be gently heated with about 2 5 ml of water in the bottom until the water boils. If a rubber balloon is then quickly fitted to the top, the pressure inside will decrease as the water vapor inside gradually cools down and the balloon will be forced inside the flask due to the air pressure inside the room. If done carefully, you will end up with a balloon blown up inside the flask. If students are first shown the balloon in the flask and asked how it was done, they will soon discover that it is not a simple task and will be very receptive to find out how it was done. The explanation is very simple. As the water was boiled, steam forced most of the air in the flask out. After the balloon is placed on the top, the air cannot reenter. So, as the temperature in the flask begins to drop, the steam condenses back into water leaving a lower pressure inside the flask than outside. This is what causes the balloon to be pushed into the flask."
Source: Cool Science Demos from the Institute of Chemical Engineering [ICE] Workshops, University of Northern Colorado.
See also the SMILE lesson on Air Pressure, using balloons and flasks: ch9302.html
Karlene then related these balloon phenomena to the Ideal Gas Law, P V = n R T. When the balloon is put over the flask with trapped steam inside, the pressure P inside is the same as that of the outside air. As the gas inside cools, steam condenses [number of moles n decreases], and pressure on the inside is reduced with decreasing temperature T. The greater air pressure outside (in the room) pushes the balloon into the flask and inflates it. When the flask is heated again, steam is again created [number of moles of gas increases]; thus the pressure increases, pushing the balloon outside the flask.
Another Five (*****) Star job by Karlene!
Fred Schaal (Morgan Park HS Math -- Visitor)
Redwings and Grackles
On a long bike ride last weekend, Fred was surprised that he didn't see any Redwings and Grackles, which habitually arrive here in the early Spring. Can anybody explain this? [It may be that 15 February is still part of meteorological winter, and even though there is a warming spell here, that may not be sufficient to attract these birds.]
Note by PJ: Check the website The Thoughts of Backyard Birds, by Mary S Van Deusen: http://www.iment.com/maida/birds/, which also contains her poetry, including the following one:
They flock for safety, hiding here in secret refuge from the hawk,
while I, behind my bedroom blind, share unbeknownst their private talk.
-- Mary S Van Deusen
Fred also explained that he often picks up fallen branches that happen to have buds on them, brings them home, puts them with water in a vase, and waits for the bulbs to open within a few days. He has had trouble in making this work the last few times, and asked whether anybody knew of a "trick substance" to add to the water to improve the likelihood of success. Any suggestions? We then had an extensive discussion as to the best way to get an Amaryllis Bulb to sprout inside the house in winter. Good, Fred!
Note added by PJ: The following information is an excerpt from the website The Joys of an Herb Garden: http://www.orchardsedge.com/articles/herb-and-flower-gardening/herb:
... "In winter, indoor space is used to start new seedlings or cuttings to be placed outside in the spring, using natural sunlight to ripen the plants. This routine will provide at least 3 outdoor/greenhouse harvests per year. If more space is available to constantly be starting indoors and flowering 2nd harvest plants outdoors, harvests are possible every 60 days in many areas, with a small indoor harvest in the winter as a possibility as well.
The basic strategy of year round production is to understand the plant has two growth cycles. At germination the plant enters into a vegetative state and will be able to use all the continuous light you can give it. This means there is no dark cycle required. The plant will [... photosynthesize ...] constantly and grow faster than it would outdoors with long evenings. Photosynthesis stops during dark periods and the plant uses sugars produced to build during the evening. This is not a requirement and the plant will grow faster at this stage with continuous photosynthesis (constant light)." ...
That website contains quite detailed information of relevance. For sprouting Amaryllis Africanus bulbs, check out WINTERTIME BULB TALK: http://www.dutchbulbs.com/bulbs/ or Forcing Bulbs for Early Winter Cheer: http://www.johannsens.com/newsletters/page3fall97.html.
(St Edwards School)
Handout: Our Bodies
Therese began by talking about the human skeleton, and its various types of joints. We first made a model for a "hinge joint", (such as the ankle) making the pieces by cutting an index card, and attaching them with a metal fastener, as shown:
______This represents the fairly rigid structure provided by bones. Now we attach the more flexible "muscles", which consist of two strands of yarn passing through the holes, and attached at the joint with tape:
|o o | < -- holes
| | |
X= fastener-->| X | |
______We then extended the process by attaching a knee joint and thigh muscles:
|o o |
|. . |
. |. . |
. = yarn -- > |. . | < -- yarn
. |. . |
|. . | |
H = tape -- > |H X H | |
______We then made a model of the "pivot joint" in the elbow, which allows you to turn your hand from "palm up" to "palm down" positions, and back. We rolled (xerographic) white paper sheets into cylinders/tubes about 2-3 cm [1 inch] in diameter, in order to construct two long "bones", the radius and ulna. We punched holes in them and taped on yarn "muscles" in the lower arm. Similarly, we made a third bone, the humerus, for the upper arm, and attached a muscle to it. These muscles are held on their respective bones by tendons, for which we used tape, as before. Then we used yarn to make "ligaments" that attach each of the two bottom bones to the top bone [but not to each other!] at the elbow joint.
|o o |
|. . | <-- thigh bone and muscles
|. . |
|. . |
______ < -- knee fastener
|H H | (a second hinge joint)
|o o |
|. . |
|. . |
|. . |
|. . |
|. . | |
|H X H | |
She also described making a "ball and socket" joint, such as found in the hips and shoulders, using lengths of paper and a small cup.
For additional information on of making models of joints, see the website Building a Model Arm: http://www.ehow.com/how_5147963_build-model-arm.html, or the Iowa State University Science Extension Program, Science is Here: http://www.extension.iastate.edu/e-set/science_is_here/front~1.html
A pretty, phenomenological lesson, Therese!
Notes taken by Ben Stark