1. INVESTIGATING THE TERMINAL VELOCITY OF WATER DROPLETS
Haoru Liu :
East Chapel Hill High School
Summer Ventures in Science and Math 2009
Dr. Tashakkori, Mr. Miles, Ms. Shrestha

2. 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.

3. Previous methods
Using a charged droplet to induce current in loops (Gunn et al. 1948)
Developing a formula based on observations (Best 1950)

4. Purpose
To develop a simple yet accurate way to measure terminal velocity
Suitable for use in a general classroom setting

5. 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

6. Methods (cont.)
Pipette used – subdivided into 10μL segments with scale
Tip of pipette cut and widened for larger drops
Droplets were colored water

7. 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

8. 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

9. Results (cont.)

10. Conclusions Method suitable Streak measurement somewhat tricky
Effects of perspective

11. Future Work Replication with standard 30fps camera
Replication with >10000fps camera
Effect of barometric pressure

12. Acknowledgements Dr. Rahman Tashakkori Jere Miles Biva Shrestha
Alex Chin