How can you break glass with sound?

• Essentially, the glass breaks because the sound is at the right frequency. 
• Every object has a natural frequency (vibrations per second), at which it prefers to vibrate. 
• This is called the "resonant frequency". 
• If you tap a quality wineglass next to your ear, you'll hear it sing at that frequency. 
• If you stimulate the glass with a sound at that frequency, the vibrations in the glass will be much more intense than at any other frequency. 
• If they are intense enough, the glass will break. It does not need to be a very high frequency, just the right, resonant, frequency for that glass.