Question

Sound is produced when a body undergoes to-and-fro movement. However, no sound is produce
when a person waves his/her hand. Why?
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Answer 1

Answer: Movement of to-and-fro is called Ocsillation and that is the property of wave ,it can be machenical or electromagnetical

sound travel by the help of air in the form of wave

therefore you could not produce sound by shaking your hand.

Answer 2

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.