Diffusia and the Brown Movement

Content and key concepts

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Alterna · physics · 1.2
Diffusia and the Brown Movement
Brownian movement, diffusion in gases, fluids and solid bodies.
Why does the smell of spirits reach the other end of the room in seconds? Why does sugar disappear in the tea itself? The answer is the chaotic movement of molecules.
GEF · Grade 7
FOP · basic level
01
The Brown Movement
Why do the dusts dance in the light?
Robert Brown's opening.
In 1827, the nerd
Robert Brown
He saw the pollen in the water in the microscope, and he noticed that small particles of pollen were constantly and chaoticly moving, and that movement never stopped.
Reason:
Water molecules
If the impact is not balanced, the particle moves, the smaller the particle and the higher the temperature, the stronger the movement.
Meaning
The Brownian movement is a direct proof that molecules exist and are moving. It is the first observation to confirm the atomic molecular structure of the substance.
🎫
The Brown Movement — Simulation
IV-007 · Large particle among small molecules
Temperature:
300
K
Size of molecules:
3
02
Diffuse
Why does the smell of perfume fill the room?
Diffuse
Diffuse
This is the spontaneous mixing of substances caused by the disorderly movement of molecules, and the molecules of one substance penetrate between molecules.
Diffuse happens in
Gases
(rapidly)
Liquids
(slow) and
solid bodies
(very slow)
Examples
The spread of perfume, the erosion of sugar in tea, the staining of water with ink drops, the welding of metals (disphuse of atoms at the border).
Temperature Dependence
The higher the temperature, the faster the diffusion, and when the molecules are heated, they move faster and mix more intensely, so the sugar is dissolved in hot tea faster than in cold tea.
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Diffuse — A Drop in Water
IV-006 · Change temperature and observe speed
Temperature:
20
°C
C
What needs to be understood
Outcome 1
Explain the physical meaning of the topic "Diffusia and the Brown Movement" through the model, not just through the formula.
Outcome 2
To distinguish and correctly use terms: diffusion, brounov motion, heat motion.
Outcome 3
Indicate the conditions for the applicability of the law, verify units and limit cases.
T
Terms of the topic
The definition should indicate the physical meaning, not a substitute for a domestic synonym.
diffusion
Self-inflicted infiltration of particles due to thermal motion.
Brown Movement
The continuous chaotic movement of microparticles in the liquid or gas due to the impact of environmental molecules.
heat traffic
Continuous chaotic movement of particles of a substance whose intensity is related to temperature.
Temperature
Physical value describing the thermal state of the system and the direction of spontaneous heat exchange.
F
Origin and conclusion of the formulas
The fundamental law cannot be "proven" by algebras: for each record, it is stated whether it is a definition, an experimental law, or a model effect.
Qualitative theme
The main content of this topic is expressed by models, observations and causal relationships; the formula is not artificially added: quantitative laws are introduced on connected pages.
!
Model boundaries and typical errors
Error: Forget model condition
The key condition of this topic is: why does the smell of spirits reach the other end of the room in seconds? Why does the sugar itself dissolve in the tea? The answer is the chaotic movement of molecules. The Brown movement proved that molecules exist.
How to Check the Mind
The formula is only applicable after selecting the system and assumptions. Then check the unit, vector direction and result behaviour at zero or very large parameter.
Σ
Conclusion on the topic
Diffusia and the Brown Movement
Why does the smell of spirits reach the other end of the room in seconds? Why does sugar disappear in the tea itself? The answer is the chaotic movement of molecules.
Why does the smell of spirits reach the other end of the room in seconds? Why does sugar disappear in the tea itself? The answer is the chaotic movement of molecules.
The formula is applicable only after the selection of the system and assumptions.
Any numerical result shall be accompanied by a unit, a sign and an explanation of its physical meaning.
The content is consistent with the FRP on Physics of the OS/OSS 2025 and the subject matter of the current lines of the PNP: I. M. Peryškin and co-authors (7–9), G. J. Mäkishev and coauthors (10–11), and with the lines "Engineers of the Future" and V. A. Kasyanov. The original texts are not reproduced, the text of the textbooks is not reproduced.