The differences of surface tension between soap and water can really make things go! This video shows some interesting demos illustrating the Marangoni Effect. Two liquids with different surface tensions will result in a surface tension gradient, resulting in a net force. This phenomena applies to each of the demonstrations shown. Watch a demonstration of how Marangoni stress can be used to propel small boats around (the "soap-powered boat").
License: Creative Commons BY-NC-SA
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