Frequency

Whether or not you would think so, there is much physics in music. For, each note has a different wavelength and frequency. Notes with higher frequencies have smaller wavelengths than those with lower frequencies. Also, throwback to that app for that loud annoying frequency that only students were supposed to be able to hear. The reason for that is because, the older you get, the harder it becomes to hear higher frequencies, but when you're younger you can normally hear them well. So what that app would do was have a high frequency where adults couldn't hear past due to age and then they would have no clue why everyone had their hands over their ears as if they heard an annoying sound.