`Surface Tension  Amina Grant                    Shakespeare                               1119 East 46th St.                               Chicago IL 60653                               312-535-1560Objective:      Students will observe forces between the water molecules which formSurface Tension.Materials:     The following materials are for a class:          1. overhead          2. beaker          3. straight pins          4. water          5. wire (24 cm. long to make a cradle for straight pin)          6. medicine-cups (to hold 1 part Joy)          7. water soluable pens          8. liquid detergent (Joy) & Glycerin          9. square wire frame (use the same wire from cradle)Strategies:                      Surface Tension          a.  Fill the beaker with water, (each student has his own beaker and straight pin).          b.  Take the straight pin and show that it is not possible to float astraight pin on the water when it is dropped vertically into the water.          c.  Fish straight pin out of the water and dry it off or use another needle.          d.  Now hold the needle horizontally as close as possible to the surface of the water (without touching the water) and drop it.                                            Questions      1.  Why is it not possible to float the needle on the water when it is dropped vertically?      2.  Why is it not possible to float the needle on the water when itis dropped horizontally?      3.  What happened?      4.  Why did it happen?                   e.  The teacher will say, "I predict the straight pin will sit on top of the water if placed right."          f.  Give students a piece of wire, demonstrate how to make a "wire cradle" for the straight pin.          g.  Put the straight pin on the cradle lift it to the surface of thewater, remove the cradle without pulling straight pin beneath the surface.                 Question      1.  What property of the water keeps the straight pin afloat?     EXPLANATION:          When the needle is dropped vertically into the water, it pierces the water surface.  The surface tension at that very small area of the straight pin is not large enough to hold the needle afloat.  But when the needle is dropped horizontally, a much larger area of the water surface is involved.  When the cradle serves to balance the straight pin on the water surface the forces between the water molecules under and around the straight pin are large enough to hold the needle afloat. II.    At this point include a brief talk about molecules.  Use a transparency and overhead to illustrate the forces at work between the molecules.III.   The Circle Inside The Frame          a.  Make a soap solution by mixing the following liquids: 1 part Joy, 21/2 parts glycerin, and 3 parts water.          b.  Place this soap solution in the shallow container, make a soap film by dipping the wire frame in the solution and taking it slowly out.          c.  Make a small loop of thread (diam. 3-4cm), wet it in the soapsolution and lay it carefully in the soap film.          d.  Once the thread loop lies in the soap film, pierce the center of the loop with a dry object (pencil or dry finger).          e.  Slant the wire frame, wiggle it, and observe the perfect threadcircle move and travel throughout the whole frame.                 Question(s)     1.  What made the wrinkley thread turn into a perfect circle?     2.  What does this tell us about the forces working on it in the soapfilm?     EXPLANATION:          This demonstration shows that there is indeed a tension working in the soap film.  However, the surface tension of water is much greater than that of soapy water.Performance Assessment:          The performance assessment that I would use represents COLLABORATIVE          LEARNING, teacher and students evaluate an investigation.          i.e. 1.  What did we do that helped you most to find an answer?               2.  What could we have done better?               3.  What new ideas did we discover?               4.  What materials and equipment helped us most?               5.  How did we use measurements to help find answers?    Scoring Rubric:               1.  5 points:  an explanation that is complete               2.  4 points:  if student includes a diagram (a)               3.  3 points:  the response is generally correct, but the                               explanation lacks clarity.               4.  2 points:  an object identification, more than one.               5.  1 points:  the response is incorrect, wrong use of term(s)                   Conclusions:          Each project will be judged according to its relationship to the      NGUZA SABA principles of Blackness.       e.g. PRINCIPLES               1. Umoja (unity) Does project encompass at least one science area?          2. Kujichagulia (self-determination) Does the project demonstrate an              understanding of a need for Afrikan people to develop solutions for             their particular needs?          3. Ujima (collective work and responsibility) Is there evidence of              shared responsibility for the development and care of the exhibit?          4. Ujamaa (cooperative economics) Were the materials for the project             obtained using self-reliant means?          5. Nia (purpose) Is the project based on a hypothesis?          6. Kuumba (creativity) Are students able to discuss project without             reciting the written material of the exhibit?          7. Imani (faith) Is there evidence of dedication among the scientists?References:     William A. Andrews, T. J. Elgin Wolfe & John F. Eix, Physical Science, (Prentice-Hall, Canada,) 1998.     Paul G. Hewitt, Conceptual Physics 6th edition, (Scott, Foresman,) 1989     Earl Zwicker, 1992     Tiek Liem`