Diffusion

:This article is about the physical mechanism of diffusion. For alternative meanings, see diffusion (disambiguation).

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Diffusion, being the spontaneous spreading of matter (particles), heat, or momentum, is one type of transport phenomena. It is readily observed for example when dried foodstuff like spaghetti is cooked; water molecules diffuse into the spaghetti strings, making them thicker and more flexible. It is a physical process rather than a chemical reaction. In cell biology, diffusion is often described as a form of "passive transport", by which substances cross membranes.

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Matter: Matter is commonly referred to as the substance of which physical objects are composed. In physics, it is everything that is constituted of elementary fermions. Philosophically, matter constitutes the formless substratum of all things, which exists only potentially and from which reality is produced...

Particle: A particle is...

Heat: Heat (abbreviated Q, also called heat change) is the transfer of thermal energy between two bodies which are at different temperatures. The SI unit for heat is the joule....