Balloon Kebab

Put a skewer straight through a balloon to form a kebab without having to hold your ears!

What you need

What to Do

Pick a sharp kebab stick - you may want to carefully sharpen it with a knife.

Carefully push it into the balloon near the neck

Then push it out of the balloon through the thick part of the balloon opposite the neck.

What may Happen

You should hear no bang, and end up with a rather inedible kebab...

What is going on?

The first question is why does a balloon pop in the first place. The rubber in the sides of the balloon is as stretched as far as it can be so if you make a hole in the balloon all the force which should have been taken by the rubber you have broken is concentrated at the edges of the hole. This force is enough to break the rubber there, making the hole bigger increasing the force concentration, this tear keeps propagating until the pressure inside the balloon drops enough to release the tension.

Why doesn't the balloon  pop if you put the skewer in the ends of the balloon?

  If you look at a balloon carefully you will notice that the rubber around most of the balloon is extremely stretched, but at the top and bottom there is an area of thicker rubber. This means that the rubber at the edges of the hole can stretch significantly so the force is shared out over a large area and it isn't large enough anywhere to break the rubber.

 Why is the rubber completely stretched in some places and hardly stretched in others?

Rubber behaves strangely when you stretch it, to start off with it is quite stiff, then as you stretch the rubber it becomes  less stiff and then eventually very stiff. This means that the rubber in the balloon will either be completely stretched or hardly stretched at all, so you get the thin rubber in the sides and the very thick rubber at the top and bottom.

Written by Dave Ansell