INVESTIGATING THE TERMINAL VELOCITY OF WATER DROPLETS Haoru Liu : hallliu000@gmail.com East Chapel Hill High School Summer Ventures in Science and Math 2009 Dr. Tashakkori, Mr. Miles, Ms. Shrestha
What is terminal velocity? Equilibrium state caused by equal forces of drag and gravity Easily predictable for small droplets-Stoke’s law Not so for larger droplets.
Previous methods Using a charged droplet to induce current in loops (Gunn et al. 1948) Developing a formula based on observations (Best 1950)
Purpose To develop a simple yet accurate way to measure terminal velocity Suitable for use in a general classroom setting
Methods White background illuminated by blue projector at the bottom of a high drop Camera placed on top of projector, aimed at white background White paper placed on ground in front of background
Methods (cont.) Pipette used – subdivided into 10μL segments with scale Tip of pipette cut and widened for larger drops Droplets were colored water
Methods (cont.) Higher frame rate used on camera (120fps) Frames extracted using Avidemux, processed with ImageJ Velocity found by multiplying streak length by frame rate
Results Volume (μL) Streak length (in) Velocity (m/s) 20 2.85 8.69 30 2.92 8.90 40 3.06 9.32 50 3.11 9.48 60 3.14 9.57 70 3.24 9.87 80 3.28 10.0
Results (cont.)
Conclusions Method suitable Streak measurement somewhat tricky Effects of perspective
Future Work Replication with standard 30fps camera Replication with >10000fps camera Effect of barometric pressure
Acknowledgements Dr. Rahman Tashakkori Jere Miles Biva Shrestha Alex Chin