Teaching Physics with the Physics Suite

Edward F. Redish

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Blowing up a balloon

Two balloons are blown up to different sizes and connected to the opposite sides of a hollow tube. The tube has a valve to prevent air from going from one balloon to the other. The balloons are of different sizes as shown in the figure. When the valve is opened, what will happen? Explain your reasoning.
  1. The larger balloon will get smaller and the smaller balloon will get larger until they are of equal size.
  2. The smaller balloon will get smaller and the larger balloon will get larger until the smaller balloon is almost gone.
  3. Nothing will happen. They will stay the same size.

Note to the instructor: This is one of the most surprising results in the collection of simple physics demonstrations. Students aren't the only one who activate a "balancing" p-prim here!

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Page last modified October 30, 2002: M13