As waves break, we have a wonderful example of one kind of fluid wave creating another kind. Breaking water waves are creating sound waves. Listen. We're all familiar with this sound, but the physics connecting the water waves to the sound waves is not so well known. To understand that, we have to look and listen to something much smaller than water waves. Bubbles. To study that leak between sound of surf and bubbles, consider a simple experiment. Start with a glass of water and try to pour water into the glass very gently so that you don't make a lot of large bubbles. And the process is almost silent. Now pour the water more vigorously so that you do form large bubbles. And you hear loud noises. This simple experiment happens not just in the glass in front of us, but on a huge scale in the ocean in front of us. It's an illustration of the fact that most of the loud sounds that we have come to associate with water and motion, the sounds you hear in the kitchen or bathroom, or sounds out in the ocean. And most of these loud sounds are due to the formation of bubbles. We can understand why by taking the equations of fluid mechanics. Using those, we can derive a relationship between the size of the bubble and the frequency or pitch of sound the bubble makes as it is formed. Large bubbles create low pitch sounds and small bubbles create high pitch sounds. This basic physics is being used by oceanographers to better understand how waves break and how that might be influencing our future climate. But it's also being used by engineers to improve the steel making industry, to improve pharmaceuticals and chemical industries and wastewater industries. And it's being used in the medical world to better diagnose and even to treat disease. Music