Isn’t a smell something that permeates the whole air around it?
I can understand if you leave a dog in a room with, let’s say weed in a bag, the smell would definetly be stronger in the proximity of that bag.
But i’ve seen dogs smell things from miles away, how do they know where to go once they sniff that smell?
Does it work like in a cartoon where the smell of something just create a sort of path to it?
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In the direction that smell gets stronger. You are right the smell goes in all direction (assuming no wind) but that also means with distance there is less smell so you just follow the path where the smell increases.
Also thats not dog exclusive. You can do that to just on a worse level. You taking your shirt to see if the smell is coming from the shirt is doing the same thing.
The path to it like seen in a cartoon may not be far off.
Basically, smell particles in the air dissipate from the central spot (where the item is) outwards in a sort of uniform manner in all directions (barring wind and other things), so if you hold a bag of weed, as per your example, the smell will move out as a circle from you. Now if you walk in a direction the centre mass of smell moves with you, but the smell still exists on the edges of where you were stood and as you walk, but the bulk of the smell stays with/near you as you are holding the thing that smells, this will create a trail of less smell to more smell, so as the dog is tracking it just keeps focusing on getting nearer to the more smell particles to eventually find the thing it’s been smelling.
It can be sorted of replicated by holding something that smokes, it cones form one spot and if you move it around its more smokey near the thing but still smokey where it was.
Eventually the smell trial will be gone as the particles will fully dissipate or become so uniform a path cannot be found, this is seen over time, but weather and wind or heat etc. Will also affect it as it will modify the way or speed at which the particles move, usually referred to as a trail “going cold” in TV or whatever.
Edit to add (as i noticed the biology flair), the dogs ability to detect the smell is mainly just that they have more smell receptors, so can detect the smells that we can’t, thats just them having better “equipment” to do the job at hand, but the way smell particles move is to do with physics.
Mark Rober did a super in depth video which explains this https://www.youtube.com/watch?v=md75n8cyenA
It essentially boils down to that it can recognize scents as well as we can recognize faces, and the particles in the air (which is what smell is) linger for long enough for them to follow
Also, tracking dogs work in partnership with a handler, which can help them recover from a false lead, get them over barriers, etc
I read an article or book some years ago; it said that the dog’s sense of smell has been tested intensely; they have like a million smell receptors for every one that we have. The article claimed that a dog can smell where another dog has peed and determine how long ago it happened, the sex of the dog, and which way the dog was walking. A dog’s sense of smell is a massive and complex world, packed with information that we can’t access. So any subtleties in the direction of scent are like huge arrows to a dog.
And if you watch a dog sniffing something out, you’ll see their head is pointed to the ground, but darting from side-to-side – it’s a very small movement, maybe the tip of their nose is only swaying a half inch and very quickly. But they’re determining which direction the smell is stronger and homing in on that information.
I read once that they also track the difference in smell by the newly or last disturbed grass, plants and ground….in addition to the scent of the thing being tracked.
Perhaps why tracking dogs need to be trained for loops and circles
As people and animals move around, things like dead skin cells and hair fall off and leave a trail for tracking dogs to follow. You also get some scent from our breath and the oils on our skin evaporating. While a person could never pick these up unless they left a really strong odor, a dog’s nose is sensitive enough to detect lingering smells hours later.