`Surface TensionLisa C. Ingram                 Frederick Douglass Middle Academy                               543 N. Waller                               Chicago IL  60644                               (312)534-6176Objective:To understand the concept "Surface Tension", through several experiments.Designed for students grades 5 through 8.Materials Needed:Overhead projector (teacher demonstration)2 glasses of equal size and deptha bucketwaterpennies 60 per group or personbowls 2 per group or persona box of toothpicksliquid soap or detergenta box of cube sugarclear cups 1 per group or personbubble solutionbubble wands or other bubble instrumentsStrategy:Students will be asked to brainstorm what surface and tension mean.  Also, discuss where they have heard the words before.  All comments will be written on the black board.  After all demonstrations students will comeback to these comments and form a definition(s).Experiment 1:  Teacher will fill two glasses underwater.  Then take them out of the water, holding them rim-to-rim so no water escapes.  Stand the glasses on a flat surface so that one rests upside down on top of the other.  Teacher will slide one penny between the two rims.  When the coin is in place, water molecules will pull together between the rims and stop the water overflowing. Question:  Why did the water stop dripping, even though there is still an opening?Answer:  The molecules are pulling and stretching to form a skin to the water.  Thus no water can get out, unless the surface tension is broken.   Experiment 2:  Teacher will use the overhead projector to demonstrate.  Arrange toothpicks in a circle in a bowl of water.  Place a cube of sugar in the center of the circle (place bowl on top of overhead projector).  Take another bowl, arrange the toothpicks in a circle again.  This time place aa piece of soap or liquid detergent in the center (place the bowl on top of projector).  Students should observe and verbally respond, the toothpicks went toward the sugar and they went away from the detergent.Question:  Why did the sugar draw the toothpicks and why did the detergent repel the toothpicks? Answer:  The sugar sucks up water, creating a current that carries the toothpicks with it toward the center.  The soap, on the other hand, gives off an oily film that spreads outward.  It weakens the surface tension, and the film carries the toothpicks away with it.Experiment 3:  A clear cup with a drop of food coloring, should be placed on top a white piece of paper.  Near by should be a bag of at least 60 pennies. (Teacher should set these items up, as stations, in the designated area before children begin)  Explanation: Tell the students that they are going to fill their cups up to the brim with water.  They will then have someone slide pennies into the color cup of water, until the color water drips on the paper.  Tell students not to throw the pennies, they want a drip not a splash.  One student in the group should be designated to count the pennies going into the water.  They are to this until there is a drip on the paper. Question:  Why does it take so long for the water to drip?Answer:  Surface tension builds around the cup, until it is broken with a penny. Performance Assessment:Students will be asked to explain surface tension verbally.  They will also be instructed to write one or two sentences defining surface tension.`