Question

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

Answer 1

Answer:

thats because the minimum to and fro motion needed is 20 vibration per second to hear sound. human hand cannot wave 20 times in a second, so sound is not produced.

Answer 2

because we can only hear sound louder than 20hz or lower than 20000hz and waving of hand is lower than 20hz..so we are not able to hear it