Someone lights an incense stick in one corner
Someone lights an incense stick in one corner. A few minutes later, in the closed room with the fan off, Anya smells it from the far side. Anya says someone must have carried it past her or a draught blew it over. Ravi says the smell spread there on its own. Who is right?
Who do you think is right? Pick one.
The answer: Ravi is right
Why
Anya is reaching for the causes she can picture, a breeze or a person walking past, because it is hard to imagine a smell crossing a still room by itself. But the scent is made of particles, and particles are never still: they are in constant random motion, and they gradually wander outward through the gaps between the air particles until they are spread through the whole room. This spreading on its own is called diffusion, and it needs no wind; a fan only speeds it up by stirring everything at once. Picture a drop of ink in a glass of perfectly still water reaching every part with nobody stirring it. Test: open a bottle of scent at one end of a quiet room and time how long it takes to reach the far end; it always arrives. Ravi is right: particles spread by their own motion.
On Socho, you explain your thinking out loud and a coach asks about YOUR reasoning — one question a day, free, in Hindi, Hinglish or English.
Try a question on Socho →More disagreements in Particulate Nature of Matter