## Friday, August 27, 2010

### Week 5 Discussion Session Notes

This week we were graced by the presence of Alan Mark, and the running of the session this week was done by Ross. The session started off with the topic of water, in particular talking about how the equation of liquid motion seem to inaccurate (on a macroscopic level), and that CGI water seems to unrealistic because of this issue.
We then proceeded to talk about the existance of Non-Newtonian fluids and how that phenomena exists. Non-Newtonian fluids come as a result of a non-linear relationship between shear and stress forces, resulting in the inability to assign a constant viscosity to the system. It was also mentioned that they are more heterogeneous in nature.
Moving on from there, it was reiterated that a small Reynold's number gives laminar flow, while a big Reynold's number (greater than or equal to 1000) gives turbulent flow. It was agreed that the equations for the Reynold's Number and viscous friction equations were the most important ones from the chapter.
Next up were discussions of bacterial motion, and how it is a case of directed motion vs Brownian motion. Note that Brownian motion still exists even in laminar flow.
In the diagram of laminar flowing water moving around the circle, the point was raised that as the water collides with the circle, there could likely be tiny amounts of turbulent flow occuring at those points of collision, due to the force of the water hitting the circle.
A plane, despite it's size, achieves laminar flow, and doesn't require the use of turbulent flow to take off from the ground. When a plane shakes, and the pilots call out "uhh, we're experiencing some turbulent motion" that's the plane experiencing turbulent flow. On a side note here as well, a helicopter is unable to travel fast than the speed of sound, or else it will break.

Up next, a good portion of the session was spent discussing the ideas of reciprocal and periodic motion, flagella, cilia and other movement related topics.
The flapper design works only if it is flexible (like a divers flipper).
During reciprocal motion, Alan told us that laminar or turbulent flow shouldn't matter due to the random motion of surrounding particles and their random collisions with the bacterium or cilia, and that it just so happens that they exist in laminar flow.
While discussing the flagella/flagella motor, it was revealed that the motor has two oscillatory motions. One rotation can cause a group of bacteria to cluster and interfere with each other, while the other rotation causes them to disperse. This technique is how they travel more effectively and competitively to their food source, since the dominant gathering of food is diffusion.

Next up, and a charming remind for Heather, is that the release of mucus from one's lungs is actually the stationary cells that line the lung walls that collect waste material within the lungs.
Finally, we talked about the torque of an unravelling DNA, how there was worry that the force of unwinding DNA would cause it to break up in a viscous liquid (not true), and that biological movies are inaccurate i.e. "walkers"

Remember, look at Poiseuille's "Life at Low Reynold's"