PHYSICAClass 11 Physics simulations · Kinetic Theory
Brownian motion
A pollen-sized particle is jostled by invisible molecules. Its mean-square displacement grows linearly with time.
What to notice
The path is random, but hotter, thinner liquids and smaller particles spread out faster.
Key relation
D = kT / 6πηa ; ⟨r²⟩ = 6Dt
Try this
Halve the particle radius. How does the rms displacement after a minute change?
What you can change
- Temperature: 273 to 373 K
- Particle radius: 0.2 to 3 μm
- Viscosity: 0.3 to 3 mPa s
More in Kinetic Theory
- Equipartition of energy
- Pressure vs temperature
- Molecules in motion
- Maxwell–Boltzmann speed distribution
- Molecular mean free path
- Pressure from molecular collisions
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