Violin, veena, piano, and Guitar are the string instruments,that make sound with vibrating strings, and the pitch is modified by the thickness, tension, and length of the string.
Tabla and drums are used to stretched membrane is used as the vibrating part, that produced sound.
drum/tabla - the stretched membrane of the instrument vibrates to create different sounds on the basis of how hard it is struck. flute- when blown air through the holes, the air present in the air columns vibrates to make sound. guitar/ sitar- the string attached to the instrument vibrates  when struck to create various sounds.  Vibration is the cause to the working of any musical instrument ………
 i hope it helps...........