How can glass be shattered with sound?
When sound shatters glass, it breaks the glass in the usual way: by distorting the glass to its breaking point. Whenever glass is bent too far, a crack propagates into the glass from its surface (usually at a defect) and the glass tears. For sound to cause this tearing process, the sound must distort the glass substantially. An extremely loud sound can distort the glass to its breaking point in a single motion. For example, an explosion shatters windows when a surge in air pressure (which you hear as a very loud “pop” sound) exerts so much force on those windows that they bend and break. However, a moderately loud tone can also break certain glass objects by pushing on those objects rhythmically until they distort beyond their breaking points. To understand how that’s possible, recall that you can get a child swinging strongly on a playground swing either by giving the child one hard push or by giving the child many carefully timed gentle pushes. The gentle pushes transfer energy to th
