Raindrops in the lab
My next experiment for the next three weeks is to examine how water droplets interact when they hit a surface of water. The idea here is that a beaker of water acts as a droplet of infinite radius, and if the smaller droplets hit the surface of the water at a critical angle, they will not bounce off the surface, but will merge with it (aka coalescence).
The apparatus I have is a canister of compressed air, connected to a jar of water which in turn is connected to a pump. The pump’s wired up to a frequency generator that allows the droplets through at an adjustable frequency. I have a strobe light fixed on the beaker of water (not a good idea if somebody has epilepsy, which I fortunately don’t), and if I correctly adjust the frequency and the height of the beaker above the table, it looks as though the droplets are standing still in mid-air, or even travelling backwards! How cool is that?
The really cool part, from my point of view, is that I have to take photos of this happening! A camera is provided, but I’ll probably bring my own in anyway to try and snap some videos of the droplets moving “in reverse”. If I can, I’ll upload them here. Watch this space!