Question

vibrating objects produce sound. but "sound can be produced by scratching a rough surface".but here, where does any object vibrate?(since vibration is required fr an object to produce sound.

Answer 1

That indeed is a genuinely-curious question!
When you scratch a rough surface, you actually are moving your hand (nails) against the rough surface making an up and down motion which is quite similar to a vibration. Thsi is responsible for producing sound.