|MadSci Network: Physics|
Dear Casey, Common things like air, water or petrol consist of molecules: If you could look at these materials under a magnification of about 10 million times, you would see atoms - little balls - stuck together in groups of two, three or ten etc., depending on the stuff you look at. Now the molecules which make up a POLYMER, like rubber, are special in that they contain THOUSANDS of atoms, arranged normally in a linear chain- or thread-like configuration. So if you looked at them under a slightly weaker magnification, you would see a THICK TANGLE of wiggling spaghetti or a felt-like mat of fibres. Because the diameters of these fibres (AND THUS THE SPACES BETWEEN THEM) are still of the same order as that of air molecules, you can make fairly air-tight balloons from this "felt". Why should a balloon pop when pricked with a needle? The needle itself only makes a tiny hole. Only if the tension in the balloon skin is so high as to PROPAGATE THE TEAR made by the needle, the balloon pops. If the needle is inserted in such a way as to DISPLACE some "spaghetti" sideways rather than to break them, the risk of popping the balloon is much reduced. The thread molecules then fit around the needle smugly and even prevent air from escaping. I never tried it, but if you take a very sharp needle, maybe lubrify it a bit and insert it very slowly into a balloon which is not too taut... a bicyle inner tube never pops when pricked with a needle. Good luck W. Sieber
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