It sounds like rain.
Daan Leussink, Grace-Lynn Keizers, Akash Mondal, Robert-Jan Vedder & Jonas Hop
This has probably happened to you before, while waiting for a bus or train, it is absolutely pouring. Luckily, you're standing under a small roof barely keeping your clothes dry, while everywhere around you, you hear this soothing white noise, the sound of rain. Where does this sound come from? As often happens in such seemingly simple natural phenomena, the physical explanation is far from simple. Maybe you expect the sound to come from the impact of the raindrop falling onto the water surface, or maybe you have noticed the small jets that form and shoots back up shortly after a raindrop splashes into the water and think it has something to do with that, but research shows the sound instead is created by a tiny air bubble forming underwater due to the first contact with water. Our research is based on the paper: "The impact of drops on liquid surfaces and the underwater noise of rain" by Andrea Prosperetti and Hasan N. Oğuz(The Johns Hopkins University). We will try to replicate their results by making a setup of our own and use that to confirm their findings as well as do some measurements of our own.
Our research question is as follows: How does the height of releasing the drop and diameter of the drop influence the sound made after impact with the surface of the water?
According to A. Prosperetti and H. N. Oğuz, the sound falling droplets make is based on two things: The velocity of the droplet during impact as well as its size. At first it was discovered that, to create a sound, a minimum velocity and diameter was required. It was until not much later that it was discovered there was also a maximum for these two parameters.