29 July 2016


What you need:

Two similar balloons

Two sports drinks bottles


Something to cut the ends off the bottles


Cut the lock and screw ends off both bottles, keep the ends unlocked and stretch a balloon over each one.

Blow up one balloon a little and lock the cap. Blow up the other a lot more and lock.

Tape the caps together and unlock – air flows from the small balloon to the larger one and inflates it even more!

Results & explanation

The small balloon’s surface is very curved, so most of the tension in the rubber squeezes down on the air, increasing its pressure. The big balloon has a flatter surface, so the tension in the rubber mostly pulls on other rubber.

PS – Marvin & Milo are © IOP and can be freely used in schools.  Please do get in touch if you’d like to modify or use them for commercial purposes.


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