Water Splashes Viewed from Above and Below the Water Experimental Details Materials  |  Setup  |  Camera Settings  |  Computer Settings The Experiment  |  The Results Materials Nikon D1 with 55 mm lens Toshiba laptop with intervalometer program Funnel with stopcock Photogate Large, clear plastic container to hold water Flash unit Ringstands, clamps, and bars to support funnel and photogate above plastic container top Setup Distance between mouth of funnel and bottom of plastic water container: 44.5 cm Water level 6.5 cm from bottom of plastic container Dropping distance: 44.5 cm - 6.5 cm = 38 cm from funnel to water surface. Photogate position (measured from mouth of funnel) 13 cm below funnel Camera Settings Camera: Nikon D1 Lens: 55 mm Aperture: f/16 Shutter speed: 1/2 sec Film speed: ISO 400 Flash: external Vivitar 283 The camera was focused on a plumb bob that was suspended along the same vertical plane as the mouth of the funnel (and photogate).  Due to light being refracted at the water's surface, the parts of the bob above and below the surface could not be in focus at the same time.  Therefore, the focus was set so that the upper and lower portions of the bob had the same degree of clarity.  The small aperture provided the depth-of-field needed to bring both portions into sharp focus. top Computer Settings We used a parallel-port  interface and an assembly-language program on the laptop to control how soon the flash unit would fire after the photogate was triggered by a falling water drop.  This time, termed the delay time, was adjustable between 1 and 104 ms.  The interface allowed for the control of 4 outputs.  The time between outputs, termed the interval time, was also adjustable between 1 and 104 ms. The camera was connected via its electronic cable release cord to the first output, and the flash unit was connected to the fourth output.  The fourth rather than the second output was used in order to provide a greater time interval between triggering the camera and the flash unit. We originally started with a 33.3 ms interval time and 80 ms delay time.  This was to provide 180 ms between the drop's breaking of the photogate beam and the discharge of the flash unit.  We needed at least 180 ms because our Nikon D1 had a shutter lag of about that amount, and no picture would be taken if the flash fired before that time.  Triggering the camera on the first output and the flash on the fourth meant that the camera would be set off before the flash. (The 80 ms delay time was later changed to 20 ms, because the photogate was moved higher.  This increased the travel time between the photogate and water surface, so the delay time could be decreased.)  top The Experiment Our goal was to photograph the different stages of a water drop splash.  A drop of water was released from the funnel, passing through the photogate on its way into a large container of water. Because it took roughly 20 ms before the drop fell to just above the water's surface, we started with a 20 ms delay time.  The interval time was set constant at 33.3 ms.  After a picture of the drop was taken, the delay time was increased by 5 ms intervals until the last allowed delay time of 104 ms was reached.  At this point, we increased the interval time by increments of 5/3 ms, keeping the delay time constant at 104 ms.  (This was to achieve pictures that were still taken 5 ms apart.)  When the last allowed interval time of 104 ms was reached, the end of the splash was reached.  A total of 61 pictures were taken, 5 ms apart from one another.  This meant that the time from the beginning to the end of the splash sequence was 305 ms (61 ms x 5).  This is slightly greater than 1/3 of a second. top The Results View water splash animations and selected photos.