Activity 13. Photographing splashes
The interrupter-style Schmitt-triggered photogate described in the Tools section works best for this activity. Set up the interrupter about a foot above the table top. Connect the output of the photogate to the input of the delay circuit, and connect output 2 of the delay circuit to a flash unit. Adjust the photogate for maximum sensitivity. Release a milk drop just above the gate. Adjust the delay so that you can capture the drop as it strikes the table. The 0.5-uf capacitor will provide delays up to about a half second.
If you're taking photos, you may find that the splash of the milk drop is so small that you can't get a large enough image on film. In order to produce a bigger splash, drop a ball into a bucket of water. By adjusting the delay, you should be able to see the circular wall of water that forms as the ball is breaking the surface. At slightly later times, you may be able to capture the jet of water that rises vertically as the water rushes inward to close the cavity formed by the ball. If you drop the ball into an aquarium of water and aim the flash unit through the side, you can adjust the delay to see the path of the ball in the water.