Needle Through a Balloon
Have you ever seen someone pop a balloon with a needle? Is it possible to stick a needle through a balloon without popping it? The Scientist of the Week shows you how! Coat the skewer with vaseline. If you are careful, you should be able to push the skewer all the way through the balloon without popping it. Insert the skewer with a gentle twisting motion into the end of the balloon opposite the knot. Continue pushing and twisting the skewer until the tip emerges from the other end, near the knot. Why doesn't the balloon pop? The rubber in the balloon consists of many long molecules that are linked together. It's similar to the way all of the noodles in a plate of spaghetti stick together. These long molecules are called polymers; when molecules of a polymer are chemically attached to each other, it is called cross-linking. These links hold the polymer molecules together and allow them to stretch…up to a point. When the force or tension pulling on the cross-links is too great, they will break, and the polymer will pull apart. The rubber at the ends of the balloon is stretched out less than in the middle of the balloon. Therefore, there is less force pulling on it. This allows the tip of the skewer to break some polymer cross-links, push aside the molecules of rubber, and slide into the balloon. However, enough cross-links remain so that the balloon holds together.
