I saw a magic show where they put a needle through a balloon. I tried this and it worked, but only with latex material balloons. I want to do my science project on this but my teacher said it was not a good idea. I think that it is because it is science, not magic. What do you think? — J, 6th Grade
It is science. The needle is able to enter latex without tearing it because the latex molecules are stretching out of the way of the needle without breaking. Like all polymers (plastics), latex consists of very large molecules. In latex, these molecules are basically long chains of atoms that are permanently linked to one another at various points along their lengths. You can picture a huge pile of spaghetti with each pasta strand representing one latex molecule. Now picture little links connecting pairs of these strands at random, so that when you try to pick up one strand, all the other strands come with it. That’s the way latex looks microscopically. You can’t pull the strands of latex apart because they are all linked together. But you can push a spoon between the strands.
That is what happens when you carefully weave a needle into a latex balloon—the needle separates the polymer strands locally, but doesn’t actually pull them apart or break them. Since breaking the latex molecules will probably cause the balloon to tear and burst, you have to be very patient and use a very sharp needle. I usually oil the needle before I do this and I don’t try to insert the needle in the most highly stressed parts of the balloon. The regions near the tip of the balloon and near where it is filled are the least stressed and thus the easiest to pierce successfully with a needle. A reader has informed me that coating the needle with Vasoline is particularly helpful.
One final note: a reader pointed out that it is also possible to put a needle through a balloon with the help of a small piece of adhesive tape. If you put the tape on a patch of the inflated balloon, it will prevent the balloon from ripping when you pierce the balloon right through the tape. This “cheaters” approach is more reliable than trying to thread the needle between the latex molecules, but it’s less satisfying as well. But it does point out the fact that a balloon bursts because of tearing and that if you prevent the balloon from tearing, you can pierce it as much as you like.