Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: John Chapman on 15/02/2009 19:43:56

Title: What is a smell?
Post by: John Chapman on 15/02/2009 19:43:56

Can anybody tell me exactly what a smell is?

For example:

- Does smell have mass and hence weight?
- Theoretically could a smell be seen if you had a microscope with a high enough resolution?
- Does a smell always need a vector to carry it? In other words is it carried along with water or spirit, or such like, as the smelly object dries or evaporates
- If the answer to that last question is 'yes' can a completely dry object smell?
- If a smelly objects is emitting something physical does this mean that as it smells it becomes lighter in weight?
- If so will a smelly object eventually disappear?

What do you think?

Title: What is a smell?
Post by: yor_on on 15/02/2009 21:56:42

It discusses what 'smell' can be broken down into.
http://www.abc.net.au/rn/talks/8.30/helthrpt/stories/s10882.htm

And this might be of 'human' interest:)
http://scienceblogs.com/neurophilosophy/2008/08/the_smell_of_fear.php

And this of course, which is a definite answer to the question of 'quantity of smell' :)
http://www.thenakedscientists.com/HTML/content/questions/question/1870/

Title: What is a smell?
Post by: Vern on 19/02/2009 12:52:47

Quote from: John Chapman

Can anybody tell me exactly what a smell is?

Just to add to you_on's very informative links:
The thing smelled is molecules of gas that escape from the thing being smelled. In that sense, it is matter; it has weight; it does tend to deplete the object from which it escapes.

Title: What is a smell?
Post by: John Chapman on 27/02/2009 18:02:56

I don't understand. If dog poo, for example, smells then what is the gas we are smelling? And why does it smell of dog poo and not the gas?

And why does charcoal absorb smells? Does the charcoal take on weight as the smelly object loses weight. And if the smell transfers to the charcoal why does the charcoal not start smelling itself?

Title: What is a smell?
Post by: yor_on on 27/02/2009 18:13:16

You are correct, I think :)
Charcoal must take up the the molecules somehow and should then have a higher 'mass'. As for why it doesn't smell, if it did, then it wouldn't do its job

And thinking of it, it's not very clear how it works.
We can take sugarless sugar as an example.
The molecules that bind to the 'sugar' receptors for example just craves the molecules to be of a certain shape and form, as long as you can construct something 'fitting' that receptor the brain will give it the 'taste' of sugar even though it may have a totally different chemical composition.

And it doesn't explain how some of those sugar substitutes can be a thousand times stronger in taste?

Title: What is a smell?
Post by: John Chapman on 15/03/2009 18:13:12

I wiki’d activated charcoal recently for another question and, in a nutshell, it says that charcoal absorbant properties work using Van der Waals forces throughout it's incredibly large surface area. It says that "one gram of activated carbon has a surface area of approximately 500 m²".

So it must be taking on mass as it absorbs a smell.