Speed of smell

Long back, sometime during my 9th Standard in school I and my neighborhood friend tried to find out the speed of smell. The story of that so called discovery follows!

I was sitting on the gallery watching outside. Hm… You are correct; I did not have any other better activity to do that day. I got this thought on “rate at which the smell propagates”. If we have some rational value for Speed of light and sound, why there is no such value for speed of smell? May be it is there? If it is, then sure that would be included in our physics syllabus! (Ah… I din know google at that time to key-in a search). So I assumed it is not found yet!!

At that time my friend Manoj came to my home. I told him about this thought; he was thinking for a while and asked me about experimenting it!! May not be accurately possible, but still a rough figure can be found; we decided to ditch cricket and give it a try.

We took a stop watch, a measuring tape and a perfume spray. We closed all the doors and windows. He stood some 15 feet away and once I spray the scent he will start the stop watch timer. As soon as he senses the smell he will stop the timer and note down the time taken! Repeat the process with different distance, location and perfume. We came to a consensus that this would be a nice way to start.

We took the first reading and found some X feet per second as speed. Then we started unleashing our dream devils. One devil said we will become like Newton and Einstein if we can successfully find the speed of smell. Other devil said; let’s not call the unit as feet per second. It should be in Bhojs (Bhavan + Manoj). If Kg-m/s2 is Newton and N/m2 is Pascal why not speed of smell be measured in Bhojs. Very Valid!!

M: Okay, but to do this firstly we need to get a patent after finding this Bhavan?

B: Okay Manoj, we can ask help from our Physics teachers.

M: But Bhavan, it is risky to leak this out. They would just give some minor suggestions and finally steal all credits form us. We would just be projected as their assistants. Even I heard Sir CV Raman’s Nobel Prize invention was actually his assistant’s work.

B: Sir CVR is my maternal grandmother’s relative, you know! I have heard that allegation. Or even I would say it a grapevine. But sure people are not that cheap da…

M: Which era are you in da. Majority of people are trying to use and exploit whenever possible. In my cousin brother’s company, he did some new creative work and his seniors just took the credit of it. Moreover, they presented it to the manager as their work just in front of my cousin. Only option he had was to keep mum. Never say about this to anyone da. Just be silent.

B: Hm.. Okay then, let’s carry on with readings. (But in 1 hour I leaked it out to atleast 3 people. Keeping a secret is next to impossible for Bhavan!!)

After taking five set of readings, we found there was no linearity and felt some more readings can give a clear picture. A week rolled on and at different places, different time and with different perfumes, we took a page full of data. There was much of a variation. For same distance the reading was different at different location.

Then we understood something fundamental. Unlike Sound or Light, it is not a self propagating wave. It depends on the medium that carries it (air in our case). Smell mixes witht he molecules of air and is propagated through that. If the air circulation is better, the so called speed of smell is faster. But through this I can confront anyone saying speed of sound as 330m/s. It is not always so. Again depends on the air circulation. Speed of sound varies from zero to even more than 330 m/s, depending on parameters like air circulation, composition, ect. When air circulation in nil (vacuum) the speed of sound is zero!! As air circulation varies the speed of sound will change (close to 330m/s though)!!

When I first said that the speed of sound cannot be taken just like that as 330 m/s, my physics teacher was not convinced. Rather she felt I am just thinking something crazy and wasting the time of whole class. I told it depends on the air circulation and composition of air and if the circulation or composition changes, the speed of sound will change, at least by a very meager proportion. She asked me a question after hearing me. I write the word hearing specifically because; she just heard (difference b/w hearing and understanding) what I spoke. If she would have understood, the discussion would have been different. “Bhavan, when there is heavy wind (blowing from speaker to the listener) can the listener hear the person speaking with same clarity as you hear me now (in this closed room)”. Hm… I was not having an answer that time. Rather i can put it this way too. Was not interested to discuss more! Clarity is a quality parameter of sound. It has nothing to do with the speed of sound wave. In heavy wind, there is a lot of disturbance and the clarity of the speaker’s voice is lost. Clarity rather depends on the energy of the sound created. It has nothing to do with the parameter called speed, my dear teacher!! I can prove it with a small example. Sound travels faster in steel than air. Reason: density of steel in more than that in air. When air circulation/ composition changes, the density of the medium will change and will affect the speed of propagation!!