Tyrethis Penrice (Oak Park Elementary) Behavior of Matter: Handouts on Adhesion and Cohesion
Tyrethis led our discussion of these questions:

1. Q: What happens when drops of water are placed on talcum powder.
   A: We suggested "beading up", absorption, and "clumping" of talcum powder
   
2. Q: What happens to the surface of water sprinkled with pepper when detergent is dropped in?
   A: We thought the pepper grains would move away from the detergent layer.

1. Drops did form beads which, after a few minutes, had a skin of talcum powder on them. The beads formed only where talc was fairly thickly spread on the paper. We may have been seeing cohesion of H₂O to H₂O, talc to talc, or adhesion of talc to H₂O---or perhaps all of them. We would not expect the talc to H₂O interaction to be present, since beading occurs.
   
2. Initially the pepper floats uniformly spread on the surface of the H₂O .  The addition of detergent initially causes the pepper grains to move away from one another suddenly (similar to "like charge" repulsion?) and then to sink below the surface (loss of surface tension).
   
3. In a third activity a glass was filled to the top with H₂O so that there was a "surface bulge" over the edge of the glass.  A cork was then floated on the surface.  The surface tension kept the cork near the center of the glass, far away from the edges.

Karlene Joseph (Lane Tech HS) Handout: Cell Diversity
Karlene started by asking "What types of cells are there?"
Frana  mentioned animal and plant cells.  Inside the human body we have these types of cells:

Activity: Karlene distributed clumps of clay of the same volume.  Each person took a clump and molded it into shapes corresponding to the shape of a given type of cell.  Here are some examples:

• Skin Cells (flattened).  This makes sense, because skin cells are used as a cover.
  
• Muscle Cells (elongated):  They contract and relax in the direction of movement.
• Red Blood Cells
  • Normal (disc shaped; concave): R allele
  • Sickle Cell (crescent shaped): r allele

This also led to a discussion of the sizes of various types of cells, which vary (generally) from  a few to a few dozen microns in diameter (1 micron = 1 mm = 10^-6 meters).  We considered intrinsic limitations in sizes of cells in terms of the surface area/volume ratio.  We made "clay cells" of various shapes using our clumps of clay.  Then we measured the dimensions and calculated the surface/volume ratios.  [For example, a cube of side 2.5 cm has a surface area of 37.5 cm² and volume of 15.625 cm³, so that the surface to volume ratio is 2.40 cm^-1.]  Cells need to be small so that the surface/volume ratio is large,  so that cells are able to absorb O₂, food, and other nutrients at rates required to support life.  By contrast, large egg cells already have the nutrients inside them, so that they are not limited so much in size.  (For example, consider ostrich eggs.)

Very interesting, Karlene!.  

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!

Notes taken by Ben Stark.