We know the speed of light as well as the speed of sound, but is there a speed of smell?

Question

I know it probably has something to do with a rate of diffusion or something to that effect based on the smells concentration.

Answer 1

The speed of light is constant, as is the speed of sound.

There *can* be a speed of "smell", but it is not constant. First of all, it is important to understand what smell is: smell is when a molecule (typically a smaller molecule, thus it is somewhat volatile) binds to a receptor in our nose (or a little further behind our nose). We have many receptors that are all specific for certain molecules. For instance, we all have a "vanilla" receptor in our noses. When vanilla scent is released, the vanilla molecules float through the air and arrive at our receptors. When the molecules bind to the receptor, it elicits a response of <>

Back to the speed question. In completely calm conditions, the molecule may go nowhere, in which case it has no speed! The molecule may travel quickly with a gust or breeze, in which case the speed is likely to be 5-10 feet/second. But there is no fixed (i.e. constant) speed for smell.

Hope that helps.

Answer 2

I guess the speed of smell actually depends on the rate of diffusion down a concentration gradient until dynamic equilibrium is reached. I think that varies with the wind etc. also. Therefore, I think the speed of smell varies.

Answer 3

I certainly wish there was a measurable speed of smell. Then I could avoid smelling all the bad stuff just seconds before it hit my nose. But actually, you're right. Ever been next to a friend just after they've "let one loose?" It's like thunder after lightning. You hear it, and then you have a period of time to avoid it because the methane is diffusing through the air and it will eventually reach your nose, and then it takes time for your nose to react to the smell. So, in truth, I guess there is a speed, but it varies. :)

Answer 4

Maybe,
How fast a gas (smell) diffuses in another gas can be predicted with Graham's Law, but within a closed environment. In the real world things like convection currents from heating and a summers breeze blowing through the window will alter the rate at which a detectable gas can travel from its source.

Answer 5

In ADDITION to the factors already mentioned (wind speed, diffucion of the original scent sample, etc.) you must take into account your level of perception. We get used to smells, the way our eyes adapt to the darkness. There must be a minimum level (probably expressed in parts per million) of volatile scent molecules in air that the olfactory nerves in your nose are capable of detecting. The speed of smell must be fairly slow.

The story is told of a dangerous gas used in the manufacturing process for transistors and microprocessors. New hires are warned that if they see people around them dropping dead, they are to run without asking questions.

Upon being asked what it smelled like, the safety trainer said, "It is suposed to smell like violets, but nobody really knows. The lethal concetration level is far lower than the detectable concentration level. Nobody that has ever smelled it has survived long enough to say what it smelled like."

Smell has by far the shortest-range of the long range senses. It really is not meant to protect us from enviornmental hazards (with the exception of fire.) There are too many poisonous gasses (such as carbon monoxide) and gasses that will not sustain life (like carbon dioxide) which have no scent at all.

The most important purpose for the sense of smell is to warn us when food is spoiled, preventing us dying of food poisoning. We are not fast enough to flee most forest fires and our sense of smell is not sensitive enough to give us warning in time to run.

Answer 6

Yes. The speed of smell is the length of time it takes to cast a buck-passing glance at the bloke standing beside you in the lift.

Answer 7

I remembered answering this question in answers for the speed of light, but yours is something extraordinary; the speed of smell.
Wow I wish I could have "eight sniffs per second" processing as per the neural mechanisms by which rodents use odors to guide their behavior! That's cool!

Answer 8

The speed of smell would have to do with wind, which is caused by heat moving air into convection currents. What kind of answer were you expecting? something ridiculous?

Answer 9

No. Smell is formed of chemicals in the air, and so they would move at different speeds depending on how fast the air was moving.

Answer 10

I would agree with your assumption. The concentration of the odor, speed of the air and volatility of the thing producing the odor would be the variables to consider.