Investigating Fluid Dynamics on Glass and Acrylic
Daniel Li, Betty Cai
University Transition Program
Floor Location : J 133 D

Intermolecular forces are interdisciplinary, connecting physics, chemistry, microscopic fluid dynamics, and macroscopic kinematics. By measuring the velocity of water flowing down an inclined surface and adjusting the inclination angle with three trials per angle, a relation between adhesion and inclination angle was derived.
The adhesion strength was calculated by analyzing traditional kinematics. The increase in the droplet's squeeze force on the surface (and consequent decrease in slide) was adhesion. The slide force was calculated through the kinetic energy formula, which incorporated the measured droplet velocity. KE was analogous to work, and work divided by droplet displacement yielded the slide force with adhesion. Knowing the droplet mass (0.15 mL = 0.15 g), the droplet's gravitational force (Fg) was obtained. The squeeze force with adhesion was calculated with the Pythagoras theorem with the gravitational and slide forces. The squeeze force without adhesion was the gravitational force multiplied by cosine of the inclination angle. The squeeze force with adhesion was subtracted by the ideal squeeze force to yield adhesion strength. A Python 3 program was written to automate the adhesion calculation process.
Velocity increased exponentially with inclination angle in both glass and Plexiglas, as expected through gravity's constant acceleration. Similarly, adhesion strength also increased exponentially with angle. However, adhesion increased linearly with velocity.
Adhesion strengths varied from minuscule values such as 5.60 ·10^-6 N to larger ones such as 0.00147 N. Adhesion was stronger in Plexiglas than glass, thus proving the hypothesis.