Brownian Motion: Questions and Answers

[thirdwind]

Hi all. My teacher briefly mentioned brownian motion a few days ago but didn't really go in depth. I am planning to do my final paper on this topic and I just have a few questions. Hopefully, someone can point me in the right direction.

1. Let's suppose I have a container of water and some small particles in it. If I understood my teacher right, the the particles exhibit brownian motion due to thermal interaction with the water. What would happen if I were to shine a light on that container for a little while and then measure their movement? My guess is that the particles will move slightly faster when exposed in light because of the extra energy the light provides. Is my line of thinking somewhat correct?

2. What if the particles were positively/negatively charged? Would shining light have different effects depending on charge? My guess is that the charge of the particle does not matter.

3. Last, I'm not sure if chaos theory can be applied here. Is chaos at a molecular level very different from, say, the Lorenz equations?

Thanks.

 

[Andy Resnick]

I think you have a good handle on the phenomenon- your thinking in #1 is spot on correct, #2 is generally correct-adding energy to the water will usually not cause any measurable difference (exteme examples to the contrary), but having charged solutes in water is different than uncharged solutes in water.

#3 is off base. Chaos applies for deterministic systems, not stochastic systems; the mathematical basis for diffusion (Brownian motion) is rooted in probability.

 

[thirdwind]

Thanks Andy. I will look into stochastic systems a little more.