[scientizscht (OP)]

Hello

I seem not to understand the otherwise very familiar phenomenon of diffusion.

Here it says that oxygen will travel 10cm via diffusion in... 27 days!
https://www.physiologyweb.com/calculators/diffusion_time_calculator.html

How can that be? From experience, you almost immediately smell molecules much heavier than oxygen, e.g. petrol or gas when they start leaking in the air.

So how can oxygen need 27 days to travel for 10cm?

Thanks

[Janus]

The diffusion coefficient given in the table and used in the calculations is for diffusion through water, not air.  For air, oxygen takes a bit under 5 min to diffuse.

[evan_au]

If there are air currents due to wind or temperature differences, gas molecules can move much faster than by diffusion alone.

At room temperature and pressure, the oxygen molecules themselves travel at around the speed of sound, but they travel a very short distance (around 70 nanometers) before they bump into another molecule, and bounce off with a random direction and speed.
See: https://en.wikipedia.org/wiki/Mean_free_path

[scientizscht (OP)]

The diffusion coefficient given in the table and used in the calculations is for diffusion through water, not air.  For air, oxygen takes a bit under 5 min to diffuse.

Okay but have you seen videos of releasing milk or ink inside water? Have you seen how fast it travels and paints the whole water?

[Hayseed]

There are a host of other things going on.  There are physical movements and positions that cause pressure and head changes thru-out the body.  And there is a constant low frequency sound or pressure disturbance thru out. This pulses the whole body.  You can see this with the correct frame rate.

There are temperature differences and I would guess the body solution is in a constant state of change.  Many things to consider with the living.  The living processes are not static.  They consume and excrete.