By Ted Kinsman
This is a relatively simple image of a drop of water. The images from a simple drop are dependent on the speed of the drop-- in this case the height it falls from, the viscosity or the fluid, and the depth of water the droplet falls into. The time the image is taken after the water's collision with the surface will also greatly influence the image. If the high speed flash it triggered too soon, the droplet will still be in mid-air. Too late, and the collision is over. The set up involves placing a pipette about two feet above a shallow pan of water, as the drip falls though an infrared light beam, a microprocessor starts counting time. After a specified time a high speed flash is triggered. This image represents a slice of time of 1/20,000 th of a second. This is often called freezing time, this image looks like frozen water.
The simple collision of a drip of water and a surface is actually quite complicated. The physics of this situation influences everything from an ink jet printer to an industrial water cutting jet. The fluid dynamics has fascinated many scientists over the years, but Dr. A.M. Worthington was so taken by the process that he wrote two books on the topic in 1908. These books were compiled from his earlier lectures and greatly influenced the use of high speed photography. In the coming weeks I will write more about high speed photography.