1. The problem statement, all variables and given/known data The water clock in question is this: I currently have to build a timer for my high school physics class. I plan on using a very similar design structure as shown in the video. However, I would like to know if there is a mechanism/modification I can do to this so that I can stop/greatly reduce the flow of water by pulling/twisting/switching something. My goal is to make this device acts more like a stopwatch than a timer. 2. Relevant equations No equations come to mind. 3. The attempt at a solution Currently, I'm thinking the best way to do it is to somehow block the flow of air from one of the tubes so that the water slows down to a drip. I'm having a hard time figuring out how to do it though.