I Determining diffusion coefficient of water by measuring velocities of objects moving in the water

  • Thread starter alfab
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Summary
We are attempting to determine the diffusion coefficient of a water medium by using velocities of pollen grains in the water.
Problem:
We wish to find the temperature and the diffusion coefficient of water by measuring the velocity of pollen grains in the medium, due to brownian motion and other forces.

Attempt:
We have a video clip and are using the program Tracker to measure the position of the pollen grains over time. We are using Einsteins equation for the diffusion coefficient

D = kT/γ

where k is Boltzmann's constant, T is the absolute temperature, and γ is the friction coefficient.

Using the equipartition theorem:

(1/2)m<v2>=(1/2)kT
We found:

D = m<v2>/6πηr
where η is the viscosity of the water, r is the radius of the pollen grain, m is the mass, and v is the velocity of each grain.

The issue:

After doing initial calculations we realized that using the velocities of the pollen grains give a very low temperature as the equipartition function is for the molecules of the water. Is there a way to rewrite this to get the temperature with respect to the grains.
 

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