Can you cut a hole in a single sheet of paper big enough to climb through? You aren't allowed to use glue or tape to stick it back together after you've cut it. Emily will show you how to accomplish this amazing feat ... and then explain why you've illustrated a rubber molecule as it stretches. You'll need a single sheet of paper and a pair of scissors ... that's all. Follow the instructions illustrated by the photos below and you'll make a hole in the paper you can climb through! Begin by folding the sheet lengthwise. From the folded edge, make two cuts, one at either end, almost to the edge of the sheet. Open up the sheet and cut along one side to make a doorway in the sheet. This doorway isn't big enough to climb through ... more cutting is needed! From the long edge of the doorway, make a series of parallel cuts almost to the edge of the sheet. When you're done, the doorway will have become a series of strips like in the photo above. Now reverse the sheet and cut down the length of each strip, almost to the end of each. This is what the sheet looks like when you're done. Grab an end and open it up. You'll find it makes one big loop ... ... which you can easily climb through! Rubber molecules are very long polymers. These polymers are attached at their ends ... but not their centres. This allows them to stretch while still remaining attached together. At the left is a 3D image of several molecules of raw rubber, called isoprene. Many of these molecules join together to make long strands called polyisoprene, which are polymers; rubber is made up of many intertwining strands of polyisoprene. The strands intertwine but aren't joined. (Think of a bowl of cooked spaghetti). Raw rubber by itself is too stretchy and soft to be of much use. At the right is a group of sulphur atoms forming a ring. When sulphur molecules are combined with the long rubber polymers using heat, in a process called vulcanization, the sulphur atoms attach to the ends of each rubber molecule, all along the lengths of the polymers. This increases the strength of the rubber, but still allows it some elasticity. At the right is a 3D image of vulcanized rubber. You can see the sulphur atoms (yellow) joining the strands of rubber polymers. This crosslinking helps hold rubber products together, and allows them to resume their original shape after stretching. (When you stretch something made of rubber, the molecules straighten out, but when you let go they spring right back into their normal twisted shape). The more sulphur cross-links there are, the harder the rubber. Vulcanization was invented by Charles Goodyear in 1839. Below is a diagram showing the chemical structure of vulcanized rubber. Main Page