Diffusion: Feynman's Physics Explained
Open a bottle of perfume in the corner of a still room and the scent eventually spreads everywhere — that is diffusion. No force pushes the molecules across the room; it is simply the random walk of perfume molecules colliding with air molecules, producing a statistical drift from where they are crowded to where they are sparse, driven by the ceaseless jiggling of all the atoms.
The big idea
Smells spread by pure randomness, not by any push.
Think about it
With no wind at all, what actually carries a smell from one side of a room to the other?
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