For Educators

Strange Soap
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Materials Needed

Cup; bubble solution (made from liquid dish soap and water); container for bubble solution (big enough for cup to fit into sideways); paper towels


1. Carefully cut the bottom out of the cup

2. Place or make the soap solution in the container

3. Coat the inside of the cup with soap solution by rolling the cup in the soap solution

4. Dip one end of the cup into the soap solution to create a soap film over the end

5. Observe the soap film. What happens?

6. When the soap film pops, dip the opposite end into the soap solution. What happens?


Now, explore! What happens if a film is formed on both ends of the cup? Measure the surface area of each end of the cup. What is the ratio? Is this a standard ratio for other sizes and types of disposable cups? Use the cup to blow large bubbles and compare the surface area of spheres.

What's Going On

Soap films in this experiment seek the smallest surface area possible. This is why bubbles and floating liquids on the space shuttle are in the shape of a sphere or ball. In the cup, the soap film moves from the large end to the small end because the small end has less surface area.

Ohio Content Standards

Physical Science: 3.3, 3.4
OSIC Codes: Y2002.CSC.S03.G03-05.BC.L03.I03; Y2002.CSC.S03.G03-05.BC.L03.I04
  • Added: November 29, 2011
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