No post last week, as I was driving across the country from San Francisco to my new digs in Boulder CO. As I was camping in the middle of very very very dry Nevada, I noticed something a little cool. As any science teacher can tell you, any demonstration having to do with static electricity works best on a dry day (and is a terrible failure in, say, Florida). As I was rolling up my thermarest, I saw the tiny little grains of hay from the ground were sticking to it, and sticking straight out from it like little porcupine quills.
You can do this yourself with spices, like dill. Rub a plastic comb with a piece of wool, and hold it near dill and you can watch the dill dance in the electric fields. It may very well stick to the comb, too. The comb has grabbed electrons from the wool and is negatively charged. The dill has no charge, but when it’s brought near the comb, those negative charges push away the electrons on the dill, making the near end of the dill positive and the far end negative. It’s induced a charge on the dill. So, then the positive end of the dill sticks to the comb, and the negative end strains to get away, so you get the porcupine quill effect.
The same thing probably happened with my thermarest and the hay. The thermarest rubbed against the fabric of the tent, making one of them negative and one positive (I don’t know which, but if I had a tape electroscope I could have found out — I’ll write about that later). It’s easier to charge things like this on a dry day because water on the surface of things gets in the way of electrons jumping from one to the other.