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Surface Tension - Balloons


To demonstrate surface tension in a counterintuitive way.


Two balloons with connecting tube and clamp.


Let the students vote before doing the experiment. Hold the smaller balloon on top as you release the◙clamp; then suggest that gravity pulls the air down into the lower balloon.◙




Use two identical balloons. Blow up one balloon on the tube and clamp it. Then blow up the other balloon to a different size and slip it onto the other end of the tube. Q: When you remove the clamp, what will happen?: (a) the small balloon will get smaller and the large one larger, (b) the two balloons will become equal, or (c) they will stay the way they are. A: The small balloon will blow up the larger one, and get smaller, due to surface tension effects. The rubber is thicker in a smaller balloon, and thus produces greater surface tension.


Sutton, Demonstration Experiments in Physics, Demonstration M-239. Pressure within a Bubble - Two-bubble Paradox. A. L. King and C. P. Sargent, Proceedings of the AAPT: Rubber balloons, AJP 16, 362 363 (1948). ◙Julius Sumner Miller, Pressure within a bubble, AJP 20, 115 (1952). ◙John Satterly, Replies to Inquiring Letters, AJP 20, 379-380 (1952). ◙D. R. Merritt and F. Weinhaus, The pressure curve for a rubber balloon, AJP 46, 976-977 (1978). ◙F. Weinhaus and W. Barker, On the equilibrium states of interconnected bubbles or balloons, AJP 46, 978-982 (1978). Debbie Kiladze, The Idea Bank Collat