Why are the voice of men women and children different??

We each have a unique voice because so many factors work together to produce that voice. As air passes over them, the vocal cords vibrate very quickly to produce sounds. The higher the rate of vibration, called frequency, the higher the pitch will be.

It is because people have grow by the genes (mutation) present in their body.

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this could be newton#'s law of cooling. the cooling curve is exponential