PURPOSE: To demonstrate how detergent decreases the surface tension of water.
DESCRIPTION: Fill a container with water and place it on the overhead projector. Place a loop of thread on top of the water such that it forms an irregular shape. A drop of detergent solution gently placed inside the loop with the eyedropper reduces the surface tension of the water inside the loop. The greater surface tension outside the loop then pulls the thread outward into a uniform circle.
SUGGESTIONS: Keep the thread near the center of the dish; use only a small drop of soap solution.
REFERENCES: (PIRA 2A15.00) See Demonstration Reference File for several articles.
EQUIPMENT: Glass dish with water, liquid dishwashing detergent, thread loop, overhead projector.
SETUP TIME: 5 min.
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