The Hot Chocolate Effect Explained

This is the time of year when people in the Northern Hemisphere like to enjoy hot beverages like hot chocolate. [The Action Lab] uses hot chocolate to demonstrate an odd acoustic effect. Tapping a container of hot chocolate — or even just hot water — will make a sound at a certain frequency. But if you keep tapping, the frequency of the sound will gradually increase. Don’t know why? Don’t worry, neither did scientists until around 1980.

This is a companion discussion topic for the original entry at