Coffee acoustics

The next video in my series with Cleveland State University has been posted. Suppose that you are in a restaurant when a nearby customer repeatedly taps his spoon against the cup’s interior. The tapping sends sound waves into the water, and the sound waves within a certain range of frequencies build up by constructive interference. Thus, the noise (and your irritation at the repeated tapping) can be significant. If the person then adds powdered coffee (or almost any other type of powder) to the water and continues to tap, the frequency range noticeably shifts and then gradually returns to its initial value. I am so fascinated by the physics of that shift that I have tested it out in every restaurant I have visited. Indeed, maybe that person that so irritated you was me.My video series