SHPE Foundation SHPE Jr. Chapter Curriculum Hands-on Activity Training TeachEngineering Hands-on Activity: * Surface Tension Lab TeachEngineering Digital Library: teachengineering.org

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General Advice Be prepared! Do each activity beforehand Make sure all materials are available Keep students on task Follow the time frame Be flexible Have Fun!! SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training

Surface Tension Lab Surface tension in soap bubbles Engineering focus: o Engineering Analysis Develop a test with quantitative measurements o Engineering Design Cycle: Design, Test, Evaluate Results, Redesign, Retest, etc. Learning objectives: o Develop a procedure to test soap bubbles o Explain how the procedure could be improved o Describe criteria in determining a better bubble o Experiment with concentrations of water and surfactant (soap) and additives (sugar or salt) to design the best recipe for soap bubbles SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Full Activity on TeachEngineering

Surface Tension Lab Suggested time: 50 minutes Suggested group size: 2 students/group Materials: 2-3 small paper cups per group 1 bubble wand per group water liquid soap (surfactant) sugar (additive) salt (additive) measuring cups measuring spoons plastic spoons ruler stopwatch safety goggles or glasses Bubble Surface Tension Lab Handout Why Do Liquid Jets Form Droplets (optional) Why Do Liquid Jets Form Droplets SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training

Surface Tension Lab SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Engineering Connection (Real World Application): Engineers design inkjet printers by exploiting the tendency of a continuous stream of water to break apart and form droplets. Surface tension must be finely adjusted, both for the ink to form droplets of the desired size and for the ink to adhere to the paper surface without smearing or bleeding, so part of the chemical engineering includes the "ink" formulation. Inkjet printers are also especially designed for many industrial applications, such as: o automotive coatings o decoration of curved and irregularly-shaped surfaces o printing conductive patterns with metallic particles o replacing screen printing on everything from ceramics to textiles o creating rapid 3D prototypes.

Surface Tension Lab SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Vocabulary TermsDefinitions Chemical engineering A field of engineering; chemical engineers use scientific knowledge of chemistry, as well as physics and biology, to design products for a wide array of uses. These products can range from personal care products (shampoo, etc.) to fuel to medicine. Surface tension The property of the surface of a liquid that allows it to resist an external force; caused by cohesive force; the reason why bugs can walk on water. Cohesive force A force of attraction; an attraction of molecules to each other; the cause of surface tension and the shape of water droplets. Surfactant A compound the reduces the surface tension between two liquids or liquid and a solid; soap is an example. engineering/chemical-engineers.htm ero_g.jpg erstriderEnWiki.jpg

Surface Tension Lab Surface Tension Background: o Water in a stream or jet starts out in a cylindrical column, and ends up as droplets. o Water molecules really like to stick together and that causes water to act the way it does. o Cohesive forces cause liquid molecules to be attracted to each other and they pull liquid molecules towards each other. o At the surface, the liquid molecules move to create the least surface area possible, as a way to minimize the stretching of the skin, and lower the amount of energy in tension on the surface. SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training d)

Surface Tension Lab Surface Tension Background (cont.) : o The water forms into round drops (not cubes or any other shape) because spheres are the shape with the least amount of surface area for a given volume of liquid. o Mixing soap (a surface-active agent or surfactant) with water lowers surface tension, and that's how we can create soap bubbles. With a lower surface tension, the air/liquid surface is more "stretchy." By contrast, high surface tensions encourage liquids to bead rather than spread evenly across surfaces SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training 21_Detaching_drop.jpg

Surface Tension Lab SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Activity Procedure: o Divide the class into lab groups, and send them to lab stations. o Have students use the lab handout to conduct all four parts of the lab, answering questions as they go. o Part 1: What makes a good soap bubble? Students decide how to measure whether a soap bubble is "good" or not. For example, they might measure how large the bubble is, how long it lasts, or how far it floats once it leaves the wand. o Part 2: Soap and Water Bubbles: Students describe procedures for testing mixtures of soap (surfactant) and water for their bubble-making abilities, record their results, and indicate which mixture performed best.

Surface Tension Lab SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Activity Procedure (cont.) : o Part 3: Additional Additives: Students refine their recipes by adding a third additive to the best mixture from Part 2, in varying amounts, to improve their solutions. o Part 4: Analysis and Reflection: Students describe their best soap bubble recipes and assess how their measurements and procedures could be improved. o Conclude with team-to-team presentations and discussions of lab techniques, procedures and results, and (optional) have students create summary documents.

Surface Tension Lab SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Teaching tips: o Emphasize the science concepts, vocabulary, and engineering connection; reinforce these throughout the activity o Allow students to develop testing ideas on their own first, and then ask them to share. Reinforce with students that its okay if two different groups use the same criteria for testing! o Make sure each group has a measurable, quantitative criterion. o Make sure students thoroughly wash the paper cups, measuring cups and spoons and the bubble wands with water and dry them between trials of different bubble recipes o Compare the best recipes from each group. Ask students to identify similarities and differences. o Have fun!!

Activity Takeaways Teambuilding skills o Making decisions, sharing tasks and materials Engineering skills o Engineering Design Process : design, test, evaluate, redesign, etc. o Engineering Analysis : developing a testing procedure, taking quantitative measurements, analyzing results SHPE Foundation SHPE Jr. Chapter Curriculum Hands-On Activity Training Encouragement to be creative o The activity encourages creativity in the developing a testing procedure Motivation through having fun o Introduce the activity as a fun learning experience!

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