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Diffusion applet

"...we know all atoms to perform all the time a completely disorderly heat motion, which, so to speak, opposes itself to their orderly behavior and does not allow the events that happen between a small number of atoms to enrol themselves according to any recognizable laws. Only in the co-operation of an enormously large number of atoms do statistical laws begin to operate... All the physical and chemical laws that are known to play an important part in the life of organisms are of this statistical kind; any other kind of lawfulness and orderliness that one might think of is being perpetually disturbed and made inoperative by the unceasing heat motion of the atoms..." -Erwin Schrödinger, What Is Life?, 1944

Download/view model (then chose File> Save Page As, save with .nlogo extension).


Setting up the model
To change the size of the opening click on change wall; The size is controlled by the hole-size slider beneath.

Particles may be added to both or either side of the applet. add particles distrubte particles evenly on both sides. add particles/add to left/add to right add the number specified on the number slider to the respective sides.


Running the model
go runs the model; the model can be stopped by unclicking the button. step advances the model by one time frame.

A single particle can be tracked by clicking follow/don't follow; to return to the normal view click the button again.

To control the "temperature" of the particles on either side use the temp-left and temp-right sliders above the model.

The distribution of total particles is shown in percentage form in % left/% right and is also graphed in the distribution plot.


Applet by Laura Cyckowski and Paul Grobstein, posted 9 July2008. Applet created using NetLogo, the availability of which is gratefully acknowledged.


Serendip Visitor's picture

Excellent job

Fantastic simulator. Is a very useful tool for demonstrating how molecules diffuse across membranes through protein channels.

Amanda W.'s picture


This really shows me how these particles are distributed!

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