What you need to do to break a wine glass is you need to find it's resonant frequency.
With wine glasses the resonant varies from 800 to 1500 hertz. How we got the resonant frequency was we flicked the glass.
The tone it played was the resonant frequency.
We couldn't get our glass to break, but we did manage to get it to vibrate.
While we failed in our attempt to break a glass because we were unable to generate the correct resonant frequency,
you can check out this successful experiment on youtube where they broke a glass using it's resonant frequency