At the entrance to the Centre for European Nuclear Research (CERN) stands a 2 metre tall statue of the Hindu deity, Nataraja (see above). To the unaware, it looks like something out of place: something that does not belong in one of the world’s largest scientific research institutions. But it is only one instance of the compatibility between physics and Hinduism.
I was reading today’s paper when I came across this question somebody had asked in the readers’ column: Why does a constantly rotating ceiling fan gather more dust than a stationary table fan? It was, at least, something along those lines.
Now I do not really know why I wanted to read the answer considering I knew it already, but I did and what I read rather shocked me.
The person who had answered it, no doubt an able, knowledgeable man, took to equivocation and beating around a bush that perhaps never existed. His whole argument was based on a ‘throw’ and an ‘impact’ that he referred to ever so often. He explained that dust gathering on a fan is like throwing an ice cream on the wall. The harder you throw it, the greater the impact and hence the more the volume of the ice cream blob that stays stuck to the wall.
While, at the end of this amusing explanation, we have a dirty wall, we have not really bothered to leave square one.
The idea he intended to give the readers, as far as I could, with some degree of strain, make out, was that the ceiling fan, while rotating with great force, creates great whizzing movements analogous to our throwing the hard-earned ice cream at the wall, and this in turn results in an impact on the dust particles, analogous to the ice cream striking the wall.
He also proceeds to outline that there exists another possibility; that there are many sticky dust particles that attach themselves to the fan. This seems to me to be more impossible than unlikely, for the chances are slim that there exist enough sticky particles in the air to turn a white fan brown. That is indeed what generally happens.
The answer that really helps is quite different. What happens is to be attributed to the phenomena of friction and static electricity.
As the fan blades brush against air molecules, they experience a resistive frictional force as they play around with electrons. This causes an electrical imbalance and a creation of static charges that are too small for us to take notice yet too big for the dust particles to overlook.
Remember what you used to do with your comb as a kid? Run it first through your hair and then through paper for the sheer enthusiasm you obtained when you saw the paper pieces eagerly sticking to the teeth on the comb? Your fan is no different. Only, it derives its enthusiasm in attracting particles of dust towards itself, and in turn in making you work all day, cleaning it.
A far better explanation than the one where we waste the ice cream, yes? That is because it is the right one.
So what about stationary table fans (because we find ceiling fans sufficiently mind-blowing, literally.) What happens is that, given that these are stationary, they experience no friction, no static electrical energy and hence cannot catalyse the dust particles attaching themselves to it. There is little else to be said.
If you have a better answer yet, (as opposed to this scientifically proved one,) please be so kind as to share it with us below!