Can sounds actually break glass? If so, is there a special frequency or decibel level needed?
Asked by: Brooke
Of course! Yes! Sound can indeed break glass. This is a wonderful question. What make
this a good question is that it indicates that, like many people, you do not realize how
powerful unseen forces can be. It is good that you have understood enough to articulate
this kind of question.
Try this little experiment: Fill a large balloon as fully as you can with air. Next, turn
on your CD player and hold the balloon. What do you feel? What would happen if you turned
the volume up higher; or down lower? Are there any changes to what you feel? Of course
there are! What you are feeling is the power of sound.
A fine crystal wine glass will respond to the sound in the same way as the balloon and for
the same reason. For that matter so will your least expensive ice tea glass! But with the
tea glass, and the windows and the picture frames and the computer screen and every other
piece of ordinary glass, the sound energy is never focused within the structure of the glass
itself. In other words the glass is not made with ordered molecules of glass. Now, if you
turned the volume way up I suppose you could break even these types of glass! But this
would more likely be because the sound waves themselves broke the glass by sheer force of
impact! Wow! That would be some sound! You could break other things this way too, like
your own ear drums!
The wine glass is a different story. This glass has a structure within which the sound can
become focused and as the volume is increased the vibration of the glass along these lines
of focus become greater and greater until they break. The really neat thing is that they
break all at once and the glass shatters!
Answered by: Tom Young, M.S., Science Teacher, Whitehouse High School, Texas
Yes, they can. What is needed is a sound at one of the natural (resonant) frequencies of the
object you want to break. You could find the frequency needed to shatter a wineglass, for
example, by tapping it sharply with a spoon (not hard enough to break it!) - the sound you
hear is the one you require.
You need to put enough energy into the object to actually break it, so that the amplitude
(size) of the resonant response is sufficient to propagate cracks in the material, and so
shatter the glass.
Glass is great for this, since it is brittle (Which means that there are not many energy
absorbing mechanisms in glass). The energy all goes into extending the length of cracks,
which happens very quickly and so shatters the object.
Answered by: Paul Hodgkinson, Physics Undergrad. Cambridge University, UK.