Spread some sawdust or mustard seed or send on the diaphragm of a table. Knock on the diaphragm lightly with a finger. What do you see happening so long as the tabla makes a sound ? What happens when the sound stops ?

Explanation

When the diaphragm of a table is knocked lightly, it starts vibrating. It keeps on vibrating till the sound is produced. Due to these vibrations, sawdust or mustard seeds or sand particles also show movements. But when the sound stops these particles also stop their movements.