[Virginia Tech Department of Physics]

Lecture Demonstrations


F30: Soap Bubble Films


Purpose: To demonstrate surface tension effects in liquids and in thin films of soap bubbles.



  1. Rectangular loop. Immerse loop in soapy solution to form a film across the two sections. Poke out the film in one section, and notice that the cross-wire bends toward the remaining film. You can slide the cross-wire to form any desired relative size for the films.
  2. Circular loop. Dip the loop into the solution to form a film across all sections. Poke out the center section of film, and notice that surface tension pulls the thread to form a circularly shaped hole.
  3. Cork and loop. Show that the cork floats on the surface of clean water. With the handle provided, push the cork down into the water until the circular loop is just below the water surface and the cork is below the loop. Release the device and notice that surface tension keeps the loop and cork submerged.

    To show the action of detergents in reducing surface tension, drop in a few drops of liquid detergent while the cork and loop are submerged, and notice that the loop pops out of the water.
  4. Carefully lay the flat piece of metal on the surface of a beaker of clean water. The surface tension will hold the metal on the surface. Pour in a few drops of liquid detergent. The detergent reduces the surface tension and the metal drops.
  5. Make large bubbles with the device to the right.

Equipment List: Storage Location: CHEMP 130A


Soapy solution (e.g., a mixture containing equal parts of distilled water, glycerin, and liquid detergent) C4.4
  Rectangular wire loop with thin moveable cross-wire, circular loop with threads tied across, thin wire loop attached to cork C4.4
  Beaker of clean water C4.4
  Liquid detergent C4.4
  Small flat piece of metal C4,4


Manual: None   Setup Notes: F30 PIRA #:
Manufacturer(s): Sargent-Welch, VT Other school's Demonstration web pages



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