4 - Kebab Balloon

This experiment demonstrates the effect different forces have on polymers. Sticking the kebab stick through the inflated balloon doesn't burst it...why?

What you will need

  • 1 balloon
  • 1 kebab stick - be very careful with kebab sticks as they are very sharp and could cause injury. Ask an adult to help with this stage.

How to do it

  • Partially inflate the balloon and tie it off. Do not fully inflate the balloon until you have practiced this experiment a few times.
  • Look at the bottom of the balloon and pinch where you see the dark spot.
  • Take the kebab stick and carefully push it through the area of pinched latex until it is inside the balloon.
  • Guide the kebab stick inside the balloon until it is just below the knot. 
  • Push the stick through the darker material just below the knot and it will come out the other side.
  • The kebab stick should now be sticking out of both ends of the balloon.

What is happening?

Balloons are made out of a material called latex. The latex material is a polymer which is a long chain of haphazard strands of molecules joined together. Because these polymers are cross-linked, when you let the air out of a balloon the molecules go back to where they were before inflation and the balloon resumes its original shape.

Where the balloon is stretched, the colour will be lighter and thinner. Where it is less stretched (at the bottom and the neck) it will be darker and thicker. The rubber relies on the rubber next to it to pull back and hold it in place.

If you make a hole where the rubber is stretched as far as it can go then there is nothing to hold the hole back and the pressure makes the rubber pull away. The hole gets bigger and bigger, and results in the balloon bursting.

The kebab stick will pass through the less stretched part of the balloon where the material is thicker and the molecular memory of the balloon particles will make the material try to get back to its original position. In doing this the molecules hug the stick tightly and hardly any air is allowed to pass, resulting in the balloon not bursting.

Share your experiment...

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All experiments must be conducted in the safest possible way. An adult must be present wherever it states one is required. Never do anything dangerous with chemicals or fire for your sake and those around you.