Question

Sound is produced when a body undergoes to-and-fro movement. However, no sound is produced when a person waves his/her hand. Why?

Answer 1

The minimum frequency required to hear a sound by humans is 20 Hz. Which means 20 vibrations per second. By waving his hand, a person can not produce 20 vibrations in a single second. Hence, no sound is produced when a person waves his/her hand.