Fick's Laws of Diffusion
Updated 2026-08-02
INTRODUCTION
English translation pending.
CORE DEFINITION
Fick's first law of diffusion states that the flux of a substance across a surface is proportional to the negative of the concentration gradient, with the diffusion coefficient as the constant of proportionality. The second law combines this with conservation of mass to give a partial differential equation describing how concentration changes in space and time. The framework underlies heat conduction, drug release, and semiconductor doping. Key qualification: the laws assume a continuum with many particles at constant temperature, and they fail in very small systems or where active transport dominates.
SCAFFOLDING EFFECT
Reduce cognitive load
- Read the gradient: predict flow direction and speed from the size of the difference between regions. - Design the coefficient: increase contact, permeability, or mixing to speed up transfer. - Predict equalization: expect flows to stop once concentrations level rather than continue indefinitely.
Anchor fast decisions
Random motion of individual particles produces a net movement from crowded regions toward sparse ones, because more particles happen to leave a dense region than enter it. The net flux scales with the steepness of the difference, and as the difference shrinks the flow slows, so the system approaches uniform concentration asymptotically. No directed force is required, because the gradient alone drives the process.
MINIMUM ACTION
In progress 0/1Practice this model in one real situation:
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Source support: Explicit
- zh.wikipedia.orghttps://zh.wikipedia.org/wiki/%E8%8F%B2%E5%85%8B%E5%AE%9A%E5%BE%8Bverified
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