Soap bubbles, balloons and marshmallows expand when placed in a vacuum. 


Teachable Topics 
  • Vacuums
  • Pressure  

The size of an object is often a trade-off between the internal pressure of the object and the external pressure acting upon it.  For objects with less-than-rigid boundaries, the size will change to equalize the pressures within and without.
In the case of a soap bubble, the size depends on the pressure of the air inside, the surface tension of the bubble's film, and the external pressure from the surrounding atmosphere.  If the atmospheric, eternal pressure decreases, then the internal pressure of the bubble will be able to push the bubble outward until the two competing effects even out.

  • Thick-walled glass flask
  • Rubber stoppers of appropriate size to plug the flask
  • Hand pump
  • Objects (such as soap suds, balloons, etc) 

  1. Place the object under consideration inside the flask and then seal it.
  2. Operate the hand pump to lower the pressure inside the flask.
  3. Watch how the lower pressure affects the object size.


Make sure that your flask of choice is string enough so that it will not shatter or break under lowered pressure.  You do NOT want to see the flask change size!

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