Experiment
Balloon on a skewer
Curriculum objectives - Science:
- explore and describe observable properties of various objects, materials and substances and sort by properties
You need:
- A balloon
- A knitting needle
This is what you do:
Blow up a balloon to about half its size.
Poke a small hole in the end of the balloon where the plastic is thickest. If the knitting needle is too thick, you can use a small needle and quickly insert the knitting needle into the hole.
Insert the knitting needle all the way through the balloon and out again next to the knot.
Can you do it without the balloon bursting?
Observe and explore:
- Try with more pins.
- Experiment with smaller and larger balloons.
- How many balloons can you fit on a stick?
Record your observations.
Pushing a skewer through the middle of a balloon is impossible unless you have some tape.
Place a small piece of clear tape in the middle of the balloon. Place the sharp point of the skewer in the middle of the tape and carefully push the end of the skewer into the balloon without bursting it!
Try it again, but on the other end of the balloon.
What is going on?
This experiment shows the strength properties of the rubber used in the balloon. Latex rubber is extremely elastic but has very little strength.
Rubber is made of many long threads or chains of molecules. These long strands of molecules are called polymers, and the elasticity of these polymer chains causes rubber to stretch. When the balloon is inflated, these strands of polymer chains stretch, particularly in the center of the balloon.
Balloons are also made with thicker top and bottom materials. The long strings of molecules stretched around the spear and hold the air inside the balloon. The extra thickness of latex rubber and the elasticity means that you can stick a stick in the balloon without bursting it.
The secret to making this experiment work is to use the part of the balloon where the rubber molecules are under the least possible strain.
