High School SMILE Meeting
24 January 2006
"A Duke arrives at a train station every day at 5 PM. He is met by his driver and taken home. One day the Duke catches an earlier train and arrives at the station at 4 PM and starts walking towards his home. The driver picks him up on the road and he arrives home 20 minutes sooner than usual. Assume the car and the man travel at constant speeds. For how long did the Duke walk?"Can your students solve this problem?
Ben Stark (Professor of Biology,
Measurement of the oxygen content of air
Ben repeated a demo done at the Biology Chemistry SMILE meeting of 09 September 2003: bc090903.html. It is a version of the classic experiment in which a candle is burned in a saucer containing water with a beaker over it, and the water rises inside the beaker. Here is a copy of that description:
The result is remarkably accurate -- particularly in the light of the following effects:
Ben showed us a simple method to calculate the amount of oxygen in air, which also demonstrates the need for oxygen in air to support combustion. He placed a candle upright into a shallow dish containing a little water, and put an inverted beaker over the candle, in such a way that the mouth of the beaker was completely underwater. He marked the initial water level of the beaker, and determined V1, the volume of air in the beaker, as the total volume of the beaker, VT, minus the volume of water initially in the beaker, minus VC, the volume of the candle above the water level. He obtained V1 = 310 ml. He then removed the beaker, lit the candle, and replaced the beaker. As the candle burned, the level of water inside the beaker gradually rose. After the candle flame went out, he again measured the volume of air in the beaker, obtaining V2 = 287 ml. He then calculated the ratio V2 / V1 = 0.93. Ben next used the perfect gas law, P1V1 = n1 RT1 and P2V2 = n2 RT2 along with the fact that the pressure and temperature should be about the same before and after: P2= P1 and T2= T1. Thus, n2 / n1 = V2 / V1 = 0.93. Therefore, in the process of consumption there has been a 7% loss in the number of moles of gas. How come?
In burning wax, a hydrocarbon with a string of CH2 monomer units, the basic (approximate) chemical reaction is
2 C H2 (wax) + 3 02 (gas) ® 2 C02 (gas) + 2 H20 (liquid)In other words, we convert 3 molecules of oxygen gas into 2 molecules of carbon dioxide gas. So that the reduction in the number of oxygen molecules is three times the net reduction in the number of gas molecules. Thus, we estimate that 21 % of the molecules initially in the air were oxygen molecules expended in the process of combustion. This result is amazingly accurate!
Note: One must measure the volumes of the beaker, water, and candle carefully both before and after the candle burns to get precise results.
A breath of fresh air for us all! Thanks, Ben!
Don Kanner (Lane Tech,
Siphoning the net
Don gives students in his classes a chance to redeem themselves over the Christmas holidays. He asks them to write paragraphs on 26 items, such as A: Atwood's Machine, and S: Siphon. Students should also find a picture describing the item, as a way of learning to use the internet. As examples of how such searching can lead to confusion and misunderstanding, Don showed a picture of a siphon found on the net, and the explanation (text) at this site was riddled with spelling errors—not a good example for kids. Two other sites had incorrect explanations of how the siphon works. Cecil Adams (http://www.straightdope.com/columns/010105.html) had a rather complete explanation of how siphons work.
Chris Etapa (Gunsalaus
Get a grip
Chris brought a group of three "artificial arms" that had been made by students in the Get a Grip program, in which Chris has participated the last two years. It is sponsored by the Bioengineering Departments at UIC and Northwestern U. The hypothetical background is that the artificial arms are made for a farmer and have to be made from everyday materials (supplied in a box to each team along with a screwdriver and hammer as the sole tools), because the farmer lives in a poor country. They are supposed to be designed so that the farmer can return to his farming tasks. The arms are scored on both functionality (picking up and carrying a bucket of water, picking up olives) and low cost. The following statement of the Engineering Challenge appears on their web page:
"Students are faced with one of two challenges that help them learn concepts of engineering. One group focuses on designing a prosthesis that will help people in third-world countries to pick up and move a bucket of water. The other focuses on designing a prosthesis that will allow people in third-world countries pick up and eat grapes without damaging them. Prosthesis will be built with materials from local hardware and department stores that mimic what is available in third-world countries. Their challenge is to use these materials to build suitable prototypes. They test them in the classroom and report their findings at the end of the program."Chris brought in three arms that were the prize winners, and all of them were very impressive, showing great ingenuity on the part of the students. Contact Professor David Schneeweis http://www.bioe.uic.edu/BIOE/BioeCoreof the Bioengineering Department at UIC if you are interested in participating. Great stuff! Thanks, Chris.
Debbie Lojkutz (Joliet West HS,
Einstein's Big Idea
Debbie brought an activity from the teachers manual of the Einsteins Big Idea program; it demonstrates potential and kinetic energy, specifically the conversion of potential to kinetic energy. Debbie had some ordinary flour placed into plastic cups into which she dropped marbles from various heights above the flour (that is, various potential energies). Each marble, when dropped, would go different depths into the flour; the depths could be measured by using drinking straws, which could be inserted into the flour until they touched the (submerged) marble. (But, shouldn't we measure the distance to the bottom of the marble?) This measurement can then be used to estimate the force stopping the marble in the flour. The depth into the flour should increase with height of the drop. Is it linear, or what? Thanks for the ideas, Debbie!
Roy Coleman (Morgan Park HS,
Ann Brandon is a "cover girl" on the 75th anniversary issue of the The Physics Teacher! Roy has been judging science fairs the past week, and ran across a problem with zeroes, specifically a girl who stated that there are currently 750 people in the world who speak English. A couple of weeks ago a student asked why wetting a cloth with water darkens the shade of the color! For a partial answer see the website: How does water change the apparent 'darkness' of many objects? by MIT physics graduate student Jason Goodman: http://groups.csail.mit.edu/graphics/pubs/wet_materials_egwr99.pdf. This is a deceptively simple question, one for us to think about and discuss in later meetings! Thanks, Roy!
Marva Anyanwu (
Wendell Green Elementary
Measure your metric knowledge and What is your nano IQ?
Marva handed out a crossword puzzle relating to the metric system, along with some clues and the solution. In addition, she distributed the quiz What's Your Nano IQ?, which appears on the National Institute of Standards and Technology (NIST) web site: http://www.nist.gov/public_affairs/kids/kidsmain.htm. You can take the quiz and determine your Nano-IQ, with the following scale:
|0 - 3||Nano Novice|
|4 - 6||Nano Nerd|
|7 - 10||Nano Genius|
Bill Colson (Morgan
Bill passed around the article Secret Science in Art by Josie Glausiusz, which appeared in the December 2005 issue of Discover Magazine: http://www.discover.com/issues/dec-05/features/physics-art-matisse-seurat/. The article contains the following introductory statement:
"Shakespeare, Seurat, and Matisse knew little about physics, but their work is awash in its principles."Bill also showed us the 08 January 2006 Foxtrot cartoon by Bill Amend, Physicists always lose snowball fights: http://yodha.livejournal.com/136964.html. Thanks, Bill.
We ran out of time before Larry Alofs could make his presentation. He is scheduled first at our next SMILE meeting, Tuesday February 07, 2006, at 4:30 pm in room 152 Life Sciences building:
Notes prepared by Ben Stark and Porter Johnson.