Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Oscillations of a Balloon


A system oscillates if it has a stable equilibrium position. The oscillation frequency depends on the inertia property (like density, mass) and elastic property, (like Young’s modules, spring constant, tension etc). This experiment gives demonstration of dependence of the oscillation frequency on elastic properties in a nonconventional system.


An empty open bottle, balloon, an empty mug, warm water in a mug.


  1. Fix the balloon at the mouth of the bottle.
  2. Keep the bottle in the empty mug. Pour warm water in this mug. The balloon inflates and becomes vertical. Keep the bottle for about a minute. Balloon will become maximum tight.
    • Question: Why does the balloon flips to become vertical? (You can think in terms of buoyancy, curvature of balloon etc)
    • Question: Does the gravitational potential energy increase or decrease as the balloon flips up?
  3. With your finger, tilt the balloon on one side and release. It will start oscillating.
  4. Just look at the oscillating balloon and conceive the frequency.
  5. Put the bottle out of the warm water and leave it for few seconds. It cools down and the balloon becomes less tight.
  6. Again tilt the balloon and oscillate it.
    • Question: Does the frequency increase or decrease?
    • Question: What conclusion you draw from this observation?