PHYS 233 - Physics for Life Sciences Lab report 4 (Competition
Between Brownian Motion and Directed Forces) Purdue University
Phys 233 Lab report Section 0012
Competition Between Brownian Motion and Directed Forces Authors Abstract
Our goal for this lab is to detect the motion of our beads that undergo both random and direct motion by creating certain conditions. We use log-log plot to help distinguish between random and direct motion. Our slope for 5μm beads in 3 seconds, 2μm beads in 3 seconds, 2μm beads in 30 seconds are 1.6386, 1.2686, and 1.6842 respectively. The class average was 1.35, 1.16, and 1.60 respectively. Our group data is consistent with the class data where 5μm beads in 3 seconds, 2μm beads in 3 seconds, 2μm beads in 30 seconds are have the slope within 1-2, which tells us that there is both random motion and direct motion. By looking on our group data, we can accept our hypothesis that the larger the beads size, the more direct motion it shows, and that as time proceeds, there will be more direct motion. By looking at the class data, we can also accept our hypothesis with the same reason described above.
Introduction
Brownian motion is a random movement of a particle colliding with other molecules of the surrounding medium in the fluid. Whereas direct motion is where all particles move in the same direction within the system. Our motivation for doing this lab is to investigate the situations where both random and direct motion can be observed at the same time. We also want to know that under which condition results for one type of motion being dominant than the other. This is important because both random motion and direct motion are utilized in many biological processes such as cellular function, ion diffusion, and signaling
molecules. To do our experiment, we tilted the microscope, making one side higher than the
other. This will make the particles move in the direction towards the lower side. As for our samples, we used 2μm beads and record the movement for 3 seconds and 30 seconds each, and 5μm beads for 3 seconds. We hypothesize that the larger the silica beads are, the faster the direct motion is traveled. Furthermore, the longer the time, the faster the beads travel. This is because the mass is directly proportional to the momentum equation. Since the microscope was at a tilted slope constantly, the momentum would be higher for higher massed objects. The same idea goes with time. The longer the time, the higher the momentum would be since it is also directly related to the momentum equation. The equation states “Delta p = F * delta t. F is equal to Mass * Acceleration” so both factors of size and time show the correct assumptions here.
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