Single-drop Experimentation

While never having a student of mine pick up experiments using single drops of water, outside of looking at Faraday waves on oscillating droplets of water (on a rigid, vibrating surface), we can imagine numerous possible experimental studies. There are classic videos of a single drop falling into a plate of water, and so on. But think of a variety of different ways of looking at a single drop of water; or it could be any liquid, and do comparison studies. With enough variety and creativity, there is a good chance what you end up looking at is not something that has been studied in depth.

Experimentally, video is best way to view whatever system you choose. Be sure to have some measured distance scale in the video or picture. You will also want to know the diameter and volume of the water droplets, as well as the height from which a drop or anything else falls - you will want some measure of the impact speed based on the height and effects of air friction.

• Notice individual drops of water on car windows after or during rain falling. What determines the size of drops that are able to remain stationary on the window? One could do experiments where different sized water drops (using pipettes to measure the volume of water in the drop) are placed on a glass surface, which is then tilted are a variety of angles. What effect does the angular tilt have on the size of droplets that are able to remain stationary? Does the surface temperature have any effect? When drops finally succumb to gravity and flows down the surface, are there any patterns that consistently appear? Add wind - use a fan or hair dryer, and what effect does this have? Use surfaces of differing materials, to see what role surface plays on the behavior of drops. 
• if you have any high-speed camera capabilities, what do single drops look like when they fall and hit hard surfaces? What are the splash patterns of single droplets of differing sizes/volumes? Does temperature make a difference? Does surface material make a difference? Is there any momentary flow of the water from the droplet along the surface before splashing happens? Does it make any difference if the surface is tilted through some range of angles? What happens if there is a single grain of sand or other material at the location of where the drop lands? What if there are small divots/craters on the surface where the drops land? Can you suppress the splash of single drops  by using different materials/topologies of the surfaces? 
• For drops of water sitting on a surface, what happens if a single grain of sand falls into the drop? Is there splashing? Are there 'ripples' or waves on the surface of the drop due to the impact of a grain of sand? What about using drops of other liquids? Grains of materials other than sand? 
• For any of the above experiments, what if the surface vibrates or moves in any way? 

Be creative, and keep thinking of variations on a theme, and make your experiments something new!