sound help?

Question

so sound is made by vibrations, then why is it that when we wave our hands, we can not hear anything? the air is also disturbed by our hand. What's going on?

Answer 1

We don't hear it simply because the human ear has receptors that can detect sound frequencies ranging only from 16 vibrations to 20,000 vibrations per second.
The sound range of hands waving in the air falls in the range somewhere between 5-12 Hz.

The depth of our hearing range does not extend to the frequency level required to be able to pick up that particular sound which is beyond the human range of 20-20,000 Hz.

A highly sensitive microphone capable of detecting low frequency outside/below the human range of 20 Hz. can very easily pick up the sound, proving that sound is indeed created by the action you describe.

Therefore, if the human eardrum and auditory receptors had the sensitivity of that microphone, we would then be able to very clearly hear the sound of our hands waving in the air.

Remember we are only talking about the human auditory condition, many animals can hear ultrasonic frequencies; dogs, for example, can hear sounds as high as 50,000 Hz, and bats can detect frequencies as high as 100,000 Hz.
So, at the other end of the frequency scale, sounds that humans cannot detect because they are limited to 20,000 Hz, an animal, such as a dog with a range of 50,000 Hz., is easily able to detect sound in that range (e.g. the whistle that "only a dog can hear and is undetectable by humans.")

Answer 2

your hands are not vibrating at a high enough frequency.

I guess if you could move then say 60 times a second (really fast) you might hear something.

Sound waves start at about 30 hertz (cycle per second) and go up to about 20,000hertz or so for humans.

It is move than just making the air move sound does not make the air move. Sound uses the air as a transmission medium.

It is an interesting question. I just am not in the frame of mind to clearly think about the physics behind it all.