When a pupil plays flute in classroom why does the window vibrate?

When the pupil plays the flute in the classroom, the flute produces a sound. This sound consists of a series of different frequencies, due to the different pitches that can be played. When these sound waves reach the window, they cause the glass in the window to vibrate according to the frequency of the sound waves. This vibration can cause the window to shake, or even to shatter if the sound is loud enough and at the right frequency. The same effect can be seen in other objects around the room, such as mirrors and pictures, which can also vibrate when sound waves hit them.